"But the book is licensed under the CC-BY-SA license, which means that the LaTeX source is also available"

Imho, updating is great - picking particular snapshots for "release" is also great (whether releases like in software, or marking and emphasizing certain versions like the German Wikipedia). I guess I can even see books where it might be sensible to prevent the marking of further releases. Deleting the changelog and VCS history (or set of diffs, or in the case of physical books - destroying the old versions) is not great, which is what was done in 1984.