Any significant textual differences between the 1954-5 Lord of the Rings and later editions?

Question

I know that Tolkien made meaningful changes to the content of The Hobbit — both in the 1955 second edition and the 1966 third edition — to align it better with the world and plot depicted in The Lord of the Rings.

What I'm wondering is whether the text of The Lord of the Rings itself has changed from edition to edition, whether to harmonize it with other published works (the Silmarillion, later reference works published by the estate...) or for other reasons. This includes the appendices.

Answer 1

Tolkien made a set of major revisions to The Lord of the Rings in 1965 (around the same time as the 3rd edition Hobbit).

In 1965, due to a technical problem, the copyright had expired on The Lord of the Rings in the U.S., and an unauthorized edition was being printed by a different publisher. Tolkien was therefore asked to revise The Hobbit and The Lord of the Rings so that new editions could be published and copyrighted. This became what is now known as the Second Edition of The Lord of the Rings, and the Third Edition of The Hobbit.

The Second Edition of The Lord of the Rings had three new sections in the book:

• "Forward to the Second Edition" was added, replacing the earlier, more in-universe, forward from the First Edition.
• "Note on the Shire Records" was added to the end of the prologue, expanding on material that used to be in Appendix A (personally I feel this one was very poorly inserted, as the text right before it is clearly meant to lead into Chapter One.)
• A very minimal index was added to the back, compiled by Nancy Smith and Baillie Klass (later Christopher's wife)

A ton of individual content changes were also made throughout the text of the book, its maps, and its appendices, on a scale similar to the third edition Hobbit, and far too many to list here.

Of particular note:

• The essay "The Palantiri" published in Unfinished Tales was created while Tolkien was working on changes for passages involving the palantirs.
• The commentary in The History of Middle-earth and The Lord of the Rings: A Reader's Companion frequently refer to changes made in the second edition. Doing some ctrl+f's show 75 occurrences of "Second Edition" in the HoMe volumes about LotR, and 240 occurrences in the Reader's Companion.

Tolkien has also made plenty of minor corrections whenever he'd spot mistakes, a practice that was continued by Christopher and by other Tolkien scholars.

Whenever a book gets re-typeset mistakes will creep in. The Lord of the Rings has had many editions, and thus many such errors. The long and complicated history of this has been summarized in the "Note on the Text" by Douglas Anderson, which appears in most editions of The Lord of the Rings starting with 1987, and updated in 1993, 2002, and 2004.

The textual history of The Lord of the Rings, merely in its published form, is a vast and complex web. In this brief note I have given only a glimpse of the overall sequence and structure.
_{Note on the Text}

For the 50th anniversary of the book, a large scale edit of the book was made by Wayne Hammond and Christina Scull, with the assistance of Christopher Tolkien.

In this edition of The Lord of the Rings, prepared for the fiftieth anniversary of its publication, between three and four hundred emendations have been made following an exhaustive review of past editions and printings.
_{Note on the 50th Anniversary Edition}

Again, a full list of these changes is well beyond the scope of this answer, but a summary can be found in the "Note on the 50th Anniversary Edition", included with most editions made after 2004, and a full list with commentary can be found in The Lord of the Rings: A Reader's Companion.

Some of the changes include:

• Fixing additional errors that entered during reprintings (including 60 errors that were introduced in the 1954 second printing and remained undetected previously)

• Standardizing spellings and capitalization where it seemed that Tolkien had a clear preference but had missed a few cases.

  A controlled amount of regularization also seemed called for, such as naught rather than nought, a change instituted by Tolkien but not carried through in all instances; Dark Power rather than dark power when the reference is obviously to Sauron (or Morgoth); Barrow-downs by Tolkien’s preference rather than Barrowdowns; likewise Bree-hill rather than Bree Hill; accented and more common Drúadan rather than Druadan; capitalized names of seasons when used as personification or metaphor, according to Tolkien’s predominant practice and the internal logic of the text; and Elvish rather than elvish when used as a separate adjective, following a preference Tolkien marked in his copy of the second edition of The Lord of the Rings. In addition, we have added a second accent to Númenórean(s), as Tolkien often wrote the name in manuscript and as it appears in The Silmarillion and other posthumous publications.
  _{Note on the 50th Anniversary Edition}

• Fixing errors that Christopher Tolkien noted in The History of Middle-earth were leftovers from previous drafts.

  Most of the demonstrable errors noted by Christopher Tolkien in The History of Middle-earth also have been corrected, such as the distance from the Brandywine Bridge to the Ferry (ten miles rather than twenty) and the number of Merry’s ponies (five rather than six), shadows of earlier drafts. _{Note on the 50th Anniversary Edition}

• Replacing the Second Edition index with a full index

Answer 2

It seems from the Note on the Text that the only corrections on the text of the actual novel were spelling, e.g.

In the production of this first volume, Tolkien experienced what became for him a continual problem: printer’s errors and compositor’s mistakes, including well-intentioned ‘corrections’ of his sometimes idiosyncratic usage. These ‘corrections’ include the altering of dwarves to dwarfs, elvish to elfish, further to farther, nasturtians to nasturtiums, try and say to try to say and (��worst of all’ to Tolkien) elven to elfin.

but there were many corrections to the foreword and appendices over time. See here for more details