Unlike IETF RFCs, yes NIPs change. But they are in a git repo so you can track their history. Most of the changes are fixing typos or better wording, which I don't mind.

Nostr has had numerous breaking changes in the past because fiatjaf could get everybody to agree to make the change, and without the change we were kinda screwed in one way or another. So an occasional breaking change is sometimes worth it.  We changed 'p' tag conventions (although the old way is still supportable), nostr: urls versus # [ 0 ]  notation (without the spaces, it might be turned into a link), and probably half a dozen more at least.

In reading recent PRs I got the impression that people were just breaking shit left and right, that breaking changes were accelerating.  But I overstated the case.  I looked into the git history and what was actually merged wasn't that bad.

I just want a list of them somewhere so I can keep up, and I want people proposing NIPs to be keenly aware that they shouldn't be breaking things.