I am very happy that you are working on a page that collects the differences between the first edition of The Lord of the Rings and the second edition of The Lord of the Rings. Many people do not have access to the first Edition of The Lord of the Rings and do not know the differences. Some of the differences between the two Editions are mentioned in The History of Middle-earth series (in the volumes about The History of The Lord of the Rings). Since I do not know, whether you want other people to edit your Sage/First Edition page, I provide you with my contributions on the Talk page of that page.
In the first edition the text read "And thenceforward for a thousand years they lived in almost unbroken peace" without mentioning the Dark Plague, the Long Winter and the Days of Dearth. This was changed in the second edition to "There for a thousand years they were little troubled by wars ..." to "...the Hobbits had again become accustomed to plenty". In the first edition the text read "Fifty leagues it stretched from the Westmarch under the Tower Hills to the Brandywine Bridge, and nearly fifty from the northern moors to the marshes in the south". In the second edition this was changed to "Forty leagues it stretched from the Dar Downs to the Brandywine Bridge, and fifty from the northern moors to the marshes in the south". In the first edition the text read "Three Elf-towers of immemorial age were still to be seen". In the second edition "on the Tower Hills" was added after that. In the first edition the following sentence incluced "upon a green hill". In the second edition this was changed to "upon a green mound". In the first edition the sentence "Hobbits delighted in such things ..." was put in the present tense. In the second edition the sentence "Outside the Farthings were the East and West Marches: the Buckland; and the Westmarch added to the Shire in S.R. 1462". In the first Edition there was no Note on the Shire Records in the Prologue. In the second Edition a Note on the Shire Records was inserted into the Prologue (The History of Middle-earth, Vol. 12, I. The Prologue).
The first edition contained a Foreword that started with "This tale, which has grown almost to be a history the great War of the Ring, is drawn for the most part from the memoires of the renowned Hobbits, Bilbo and Frodo, as they are preserved in the Red Book of Westmarch". In the second edition of 1966 this foreword was omitted in its entirety (The History of Middle-earth, Vol. 12, II. The Appendix on Languages).
In the first edition the description of the direction of the road to Stock in the Shire did not agree with the direction of the road to Stock on the map of the Shire. In the second edition of 1966 the description of the direction of the road to Stock was changed from "bent southward" to "bent left" at that point and it was inserted "into the lowlands of the Yale making for Stock" and a text was inserted that the Hobbits took a lane that branched right to Woodhall (The History of the Lord of the Rings, Part 1, The Return of the Shadow, II FROM HOBBITON TO THE WOODY END, Note 10, p. 66).
In the first edition the text said that "The Ferry is south-east from Woodhall". This was corrected to "east" in the revised edition (second Impression 1967), when J.R.R. Tolkien observed the discrepancy with the map of the Shire (The History of the Lord of the Rings, Part 1, The Return of the Shadow, IV TO MAGOTT'S FARM AND BUCKLAND, Note on the Shire Map. p. 107).
In the first edition Finrod was called Finrod Inglor the Fair and Finrod was the name of the third son of Finwë and his son was Felagund in the appendices. In the second edition of 1966 Finrod son of Finwë became Finarfin, and his son Inglor Felagund became Finrod Felagund (The History of the Lord of the Rings, Part 1, The Return of the Shadow, X THE ATTACK ON WEATHERTOP, Note 9 p. 188).
In the first edition the "bit and bridle" of Glorfindel's horse flashed. In the second edition the "headstall" of Glorfindel's horse flashaed, because elves did not use bits (The History of the Lord of the Rings, Part 1, The Return of the Shadow, XI FROM WEATHERTOP TO THE FORD, Note 4, p. 198).
In the first edition the text said that the road runs along the river Bruinen (Loudwater) for many leagues to the Ford. In the second edition of 1966 the text was changed to read that the road runs along the edge of the hills for many miles from the Bridge to the Ford of Bruinen. In the first edition the text read "The Road bent back again southward towards the River, but both were now hidden from view". In the second edition of 1966 the text was changed to read "The Road behind held on its way to the river Bruinen, but both were now hidden from view" (The History of the Lord of the Rings, Part 1, The Return of the Shadow, XI FROM WEATHERTOP TO THE FORD, Note on the course of the Road between Weathertop and Rivdendell, p. 199).
In the first edition the text read "At this point the Road had turned away from the river down in its narrow valley, and now clung close to the feet of the hills, rolling and winding northward among woods and heather-covered slopes towards the Ford and the Mountains". In the second edition of 1966 the text was changed to "At this point the Road had left the Hoarwell far behind in its narrow valley, and now clung close to the feet of the hills, rolling and winding eastward among woods (etc.)". The changes were made to remove contradictions between the narrative and the map that existed in the first edition. (The History of the Lord of the Rings, Part 1, The Return of the Shadow, XI FROM WEATHERTOP TO THE FORD, Note on the course of the Road between Weathertop and Rivdendell, p. 200-203).
In the first edition the text read "Michel Delving south-east". In the second edition of 1966 the text was changed to read "A mile or two further south they hastily crossed the great road from the Brandywine Bridge; they were now in the Tookland and bending south-eastwards they made for the Green Hill country. As they began to climb ist first slopes they looked back and saw the lamps in Hobbiton far off twinkling ..." (The History of the Lord of the Rings, Part 1, The Return of the Shadow, XVI DELAYS ARE DANGEROUS, Note 9, p. 284).
In the first edition the text was "I did not know that any of that fairest folk were ever seen in the Shire". In the second edition this was changed to "Few of that fairest folk are ever seen in the Shire" (The History of the Lord of the Rings, Part 1, The Return of the Shadow, XVI DELAYS ARE DANGEROUS, Note 12, p. 285).
On the map of the Shire in the first edition the main road is shown as passing between the River and Brandyhall does not agree with the text on the path taken by the Hobbits. On the map of the Shire in the second edition the placement of the main road was corrected after a Fashion (The History of the Lord of the Rings, Part 1, The Return of the Shadow, XVIII AGAIN FROM BUCKLAND TO THE WITHYWINDLE, Note 6, p. 305).
In the first edition the name The Yale does not appear on the map of the Shire. In the second edition The Yale was added in relation to a small black square (The History of the Lord of the Rings, Part 1, The Return of the Shadow, XXII NEW UNCERTAINTIES AND NEW PROJECTIONS, Note 10 p. 387).
In the first edition the text read "the interwoven words in the Elven-tongue". In the second edition the text was changed to "the interwoven words in elven-tongues" (The History of the Lord of the Rings, Part 2, The Treason of Isenguard, V BILBO'S SONG AT RIVENDELL, p. 84).
In the first edition the text read "They went back to the old path on the west side of the Silverlode". In the second edition this was changed to "They went back to the path that still went on along the west side of the Silverlode" (The History of the Lord of the Rings, Part 2, The Treason of Isenguard, , XII LOTHLÓRIEN, Note 32, p. 240).
In the first edition the text read "Dreadful as the Dead Marshes had been, and the arid moors of Nomen's land (etc.)". In the second edition this was changed to "Dreadful as the Dead Marshes had been, and the arid moors of the Noman-lands (etc.)" (The History of the Lord of the Rings, Part 2, The Treason of Isenguard, XV THE FIRST MAP OF THE LORD OF THE RINGS, p. 321)
In the first edition the text read "It was not known to us that any of the palantirs had escaped the ruin of Gondor. Outside the Council it was not among elves and men even remembered that such things had ever been, save only in a Rhyme of Lore preserved among Aragorn's people". In the second edition the text was changed to "We had not yet given thought to the fate of the palantíri of Gondor in its ruinous wars. By Men they were almost forgotten. Even in Gondor they were a secret known only to a few; in Arnor they were remembered only in a rhyme of lore among the Dúnedain." (The History of the Lord of the Rings, Part 3, The War of the Ring, PART ONE: THE FALL OF SARUMAN, VI THE PALANTÍR, p. 77 and note 14, p. 80).
In the first edition the description of the topography of the land around the Gates of Mordor that could be seen from the hollow in which Sam and Frodo hid was slightly different (The History of the Lord of the Rings, Part 3, The War of the Ring, PART TWO: THE RING GOES EAST, III THE BLACK GATE IS CLOSED, Note 9, p. 128).
In the first edition the leader of the force of three thousand Riders of Rohan who were sent to waylay the West Road against the enemy that was in Anórien was not named. In the second edition it was stated that they were under the command of Elfhelm (The History of the Lord of the Rings, Part 3, The War of the Ring, PART THREE: MINAS TIRITH, IX THE BATTLE OF THE PELENNOR FIELDS, Note 16, p. 373).
In the first edition the text read "Verily, for in the high tongue of old I am Elessar, the Elfstar, and the Renewer". In the second edition Envinyater was added before "the Renewer" (The History of the Lord of the Rings, Part 3, The War of the Ring, PART THREE: MINAS TIRITH, XI THE HOUSES OF HEALING, Note 13, p. 395).
In the first edition the text Gandalf said "The clothes that you journeyed in". In the second edition of 1966 this was changed to "The clothes that you wore on your way to Mordor" (The History of the Lord of the Rings, Part 4, Sauron Defeated, V THE FIELD OF KORMALLEN, p. 46). --Akhorahil 15:32, 4 November 2020 (UTC)
In the first edition the sentence starting with "For Sam he brought a coat of guilded mail, and his elven-cloak all healed of the soils and hurts that it had suffered;" continued with "and when the Hobbits were made ready, and circlets of silver were set upon their heads, they went to the King's feast, and they sat at his table with Gandalf ...". In the second edition after "suffered;" a passage was insterted in which Gandalf brought Sting and Sam's sword and Frodo hat to be persuaded to wear a sword and to accept back Sting (The History of the Lord of the Rings, Part 4, Sauron Defeated, V THE FIELD OF KORMALLEN, p. 50).
In the first edition Ioreth calls the Hobbits Periannath. In the second edition this was changed to Periain (The History of the Lord of the Rings, Part 4, Sauron Defeated, VI THE STEWARD AND THE KING, p. 55).
In the second edition it was added that Aragorn wore a "star upon his forehead bound by a slender fillet of silver". In the first edition Faramir proclaimed Arargon as the "chieftain of the Dúnedain of the North". In the second edition this was changed to "chieftain of the Dúnedain of Arnor". In the second edition it was inserted that Faramir also proclaimed Aragorn as "bearer of the Star of the North" (The History of the Lord of the Rings, Part 4, Sauron Defeated, VI THE STEWARD AND THE KING, p. 56). --Akhorahil 11:34, 5 November 2020 (UTC)
The statement that the Riders of Rohan and the sons of Elrond left Minas Tirith on the eighth day of May was absent in the first edition and was inserted in the second edition. In the first edition Aragorn says "I may have life far longer than other men". In the second edition Argagorn says "I shall have life far longer than other men" (The History of the Lord of the Rings, Part 4, Sauron Defeated, VI THE STEWARD AND THE KING, p. 57).
Folcwine was absent in the names of the Kings of the Mark that was recited by the Minstrel in the first edition and was inserted in the second edition. The Name of King Léof was changed to Léofa in the second edition (The History of the Lord of the Rings, Part 4, Sauron Defeated, VII MANY PARTINGS, p. 68).
In the first edition Treebeard does not say when Saruman was released. In the second edition "seven days" was inserted after "Yes, he is gone". In the first edition it read "After they had passed by Dunland and were come to places where few folk dwelt, and even birds and beasts were seldom to be seen, they journeyed through a wood ...". In the second edition this was changed to "On the sixth day since their parting from the King they journeyed through a wood ..." In the second edition "Next day they went on into northern Dunland, where no men now dwelt, though it was a green and pleasant country" was inserted after "I fancy he could do some mischief still in a small mean way". (The History of the Lord of the Rings, Part 4, Sauron Defeated, VII MANY PARTINGS, p. 69).
In the second edition ", and they rode at ease until they reached the Swanfleet river, and found the old fort, east of the falls where it went down suddenly into the lowlands. Far to the west in a haze lay the meres and eyots through which it wound its way to the Greyflood: there countless swans housed in a land of reeds. So they passed into Eregion, and" was inserted between "September came in with golden days and silver nights" and "at last a fair morning dawned ..." (The History of the Lord of the Rings, Part 4, Sauron Defeated, VII MANY PARTINGS, p. 70).
In the first edition the eleventh king in the list of Kings of the Mark is called Léof by the minstrel in Edoras, but in the list of the Kings of the Mark in Appendix A (II) the eleventh king is called Brytta. In the second edition the explanation "He was called by his people Léofa, for he was loved by all; he was openhanded and a help to all the needy (The History of the Lord of the Rings, Part 4, Sauron Defeated, VII MANY PARTINGS, Note 11, p. 72).
The name of Lórien used by Treebeard was spelt Laurelindórinan in the first edition. This was changed to Laurelindórenan in the second edition. In the second addition a comma was added after vanimar (The History of the Lord of the Rings, Part 4, Sauron Defeated, VII MANY PARTINGS, Note 16, p. 73).
In the first edition in a footnote to the text the probable Orkish origin was spelled Sharkū. In the second edition the spelling was changed to Sharkû (The History of the Lord of the Rings, Part 4, Sauron Defeated, IX THE SCOURING OF THE SHIRE, Note 26, p. 106).
In the first edition the text read "One [runner] came in from Bamfurlong last night". In the second edition Bamfurlong was changed to Whitfurrows. In the first edition "We are on old Farmer Maggot's land" was changed to "This is Bamfulong; old Farmer's Maggot's land" in the chapter "A Short Cut to Mushrooms" (The History of the Lord of the Rings, Part 4, Sauron Defeated, IX THE SCOURING OF THE SHIRE, Note 27, p. 107). --Akhorahil 15:11, 5 November 2020 (UTC)
In the first edition king Ostoher was called Ostohir, king Ondoher was called Ondohir and king Ciryaher was called Ciryahir. In the first edition Angamaite was called Angomaite and Sangahyando was called Sangahyanda (The History of Middle-earth, Vol. 12, VII. The Heirs of Elendil).
In the first edition Elrond wedded Celebrian in T.A. 100 in Appendix B. In the second edition this was changed to T.A. 109 (The History of Middle-earth, Vol. 12, VIII The Tale of Years of the Third Age, Note 7).
In the first edition Elladan and Elrohir were Born in T.A. 139 in Appendix B. In the second edition this was changed to T.A. 130 (The History of Middle-earth, Vol. 12, VIII The Tale of Years of the Third Age, Note 30).
The first edition did not contain the first paragraph in the opening of Appendix A I (i) that starts with "Feanor was the greatest of the Eldar in arts and lore ..." and that talked about the history of the Silmarils, the rebellion of Feanor and the war against Morgoth. In the second edition this paragraph was inserted before the paragraph that starts with "There were only three unions of the High Elves and Men ..." (The History of Middle-earth, Vol. 12, Part One: The Prologue and Appendices to The Lord of the Rings, IX The Making of Appendix A).
In the first edition the description of the events leading to the Kin-strife in Appendix A I (iv) was much shorter than in the second edition. In the first edition the passage started with "Nonetheless it was not until the days of Rondendacil II that the first great evil ...". In the second edition this was changed to "Nonetheless it was not until the days of Valacar that the first great evil ...". In the second edition the following three sentences were added after the previously mentioned sentence "Minalcar, son of Calmacil, was a man of great vigour, and in 1240 Narmacil, to rid himself of all cares, made him Regent of the realm. From that time onwards he governed Gondor in the Name of the kings until he succeeded his father. His chief concern was with the Northmen." In the first edition the text continued with "The Northmen increased greatly in the peace ...". In the second edition the text continued with "These had increased greatly in the peace ...". In the first edition the text read "In the days of Romendacil II their attacks ..., but it was learned by the King that ...". In the second edition this was changed to "In the days of Narmacil I their attacks ..., but it was learned by the regent that ...". In the second edition the following two sentences were inserted after the previous sentence "Minalcar therefore in 1248 led out a great force, and between Rhovanion and the Inland Sea he defeated a large army of the Easterlings and destroyed all their camps and Settlements east of the Sea. He then took the Name of Rómendacil". In the first edition the text continued with "Rómendacil there fortified the west shore ...". In the second edition this was changed to "On his return Rómendacil fortified the west shore ...". In the second edition the following sentences were inserted "Rómendacil showed especial favour to Vidugavia, who had aided him in the war. He called himself King of Rhovanion, and was indeed the most powerful of the Northern princes, though his own realm lay between Greenwood and the River Celduin". In the first edition the text continued with "In return he sent his son Valacar to dwell for a while with Vidugavia, who called himself the King of Rhovanion, and was indeed the most powerful of their princes, though his own realm lay between Greenwood and the River Running. There Valacar was wedded to Vidugavia's daughter, and so caused later the evil war of the Kin-strife". In the second edition this was changed to "In 1250 Rómendacil sent his son Valacar as an ambassador to dwell for a while with Vidugavia and make himself acquainted with the language, manners, and policies of the Northmen. But Valacar far exceeded his father's designs. He grew to love the Northern lands and people, and he married Vidumavi, daughter of Vidugavia. It was some years before he returned. From this marriage came later the war of the Kin-strife". In the first edition in the following paragraph the third sentence read "To the lineage of his father he added the fearless spirit of the Northmen". In the second edition this was changed to "To the lineage of Gondor he added the fearless Spirit of the Northmen." and "He was handsome and valiant, and showed no sign of ageing more swiflty than his father." was inserted before "When the confederates led by descendants of the kings rose against him ...". In the first edition in the list of Kings of Gondor in Appendix A (I) it read "Romendacil II 1366". In the second edition this was changed to "Minalcar (regent 1240-1304), crowned as Romendacil II 1304, died 1366" (The History of Middle-earth, Vol. 12, IX The Making of Appendix A, Note on the expansion of the tale of the Kin-strife in the Second Edition).
In the second edition the opening of Appendix A was replaced with an entirely new text and a note on the Shire Records was added at the end of the prologue (The History of Middle-earth, Vol. 12, IX The Making of Appendix A, Note 2).
In the first edition there were no notes in the list of the Kings of the Mark to Brytta, Walda and Folca in Appendix A (II) (The History of Middle-earth, Vol. 12, Part One: The Prologue and Appendices to The Lord of the Rings, IX The Making of Appendix A, Note 5).
In the second edition of 1996 in Appendix B at the end of the prefatory remarks to the Tale of Years of the Second Age "Celebrimbor was lord of Eregion and the greatest of their craftsmen; he was descended from Feanor" was added (The History of Middle-earth, Vol. 12, X. Of Dwarves and Men MEN, Note 7).
In the first edition Aragorn died in Shire Reckoning 1521, i.e. F.A. 100. In the second edition this was changed to Shire Reckoning 1541, i.e. F.A. 120 (The History of Middle-earth, Vol. 12, XVI. The New Shadow, Note 7). --Akhorahil 13:34, 6 November 2020 (UTC)
In the first edition . In a later impression of the Ballantine edition of 1966 Estella Bolger as the sister of Fredegar Bolger and her birth-date 1385 and that Meriadoc married Estella Bolger was inserted to the familty trees. These additions to the family trees werde also made in the Houghton Mifflin edition of 1987. These additions were also made in the re-set edition published by HarperCollins in 1994 (The History of Middle-earth, Vol. 12, III. The Family Trees, Note 1).