In the distant past of 2008, an above-average endgame book was published called 100 Endgames You Must Know. (The king of endgame books - certainly of one-volume works - remains Dvoretsky’s Endgame Manual.) I knew there had been at least one revision, so I looked it up today and saw that the sixth edition came out last year. At least superficially, this seems to mean that there are new endings that we must know - but then whichever of the original 100 dropped out weren’t necessary after all - or that things had to be fixed - at least five times! - suggesting that the author didn’t know these “must-know” endgames as well as he was supposed to. (But don’t worry, I’m sure he’s got them right this time.)
The more generous explanation is that he has found better ways to explain some of the more complicated examples and maybe developed better exercises to help test and cement the reader’s understanding. The only problem is that there’s also The 100 Endgames You Must Know Workbook. So c’mon. If you’re sticking to 100 endgames, then get them right and be done with it. And if it takes 16 years to get it right or to figure out how to explain it to amateurs, maybe it isn’t really a must-know ending.