Does anyone know the difference between the 3rd and 4th edition of "100 Endgames You Must Know"? I just looked at the Table Of Contents and they are identical and random pages on Amazon look the same too. I would imagine there must be some new use of the new tablebases that were completed since 2012?
De la Villa's "100 Endgames you must know", though apparently a good book seems to have been plagued by an abundance of typos and mistakes as detailed in this blogpost.
So although the culprit in this case has been the 2nd edition, maybe it does make sense to go for the latest edition. Here you can look at the errata page which presumably contains errors that have now been corrected, although as I mentioned some of these corrections probably already happened in the third edition.
I have the book on Chessable (popular site for reading chess books like this one):
The difference in edition come from improved annotations and error checking. That's common for all books (chess or not). If you already have the 3rd edition, there's no point to get the newer edition.
Please note the edition is not specified in the screenshot because it's always the latest edition. I'd recommend to get an ebook version (e.g. Chessable or other publishers). New In Chess updates their ebooks for free, you will get a free update when they release the 5th, 6th edition etc.
Endgame books always contain analysis mistakes, and newer editions always correct these mistakes. So I would recommend to get up-to-date by buying the last one.
As you said, 7-men Lomonosov built since last edition, and probably 7-men tablebase revealed that some analyses wrong.
From erreta page: "On this Errata page we provide our readers with corrections in our books of analytical mistakes, or mistakes which might lead to misunderstandings ..."
I know this answer is coming late, but as someone who had the 3rd edition and upgrated to the 4th edition I can answer this definitely. The ONLY difference in the new edition is that diagrams have an indicator of who is to move, and glancing at the text below the diagram it's very easy to see who is to move if you can't already figure it out based on the particular ending you are studying, if you already have the 3rd and you want this "feature" just go through the book with a pencil and mark every diagram with W/B for who has the move, everything else in the book word for word is IDENITCAL, yes I went through each page and did not see ANY difference whatsoever. Those that said that updated versions where usually money grabs nailed this one completely. The publisher New In Chess was extremely deceptive selling this as a new version complete with a new book cover. This could have been done in a new printing, shame on New in Chess.