Don't some of your local files get replaced with "similar" tracks, e.g. your locally curated live tracks with more common ones? I think I heard that that can happen when you son your library with Apple. That scared me off years ago.
Oh, nothing like that has ever happened to me at least. But all (most) my local music is simply things not available on AM at all. However, I do know for sure that some albums that I have ripped from CD that also exists on AM have not been replaced, and they are even basically the same release.
So all the songs in my library have one of these Cloud Statuses:
Matched, Purchased, Uploaded or Apple Music.
One would think that
Matched here means "uploaded and matched/replaced", but that is for sure not the case. Even tracks that I have made myself, pre-masters not even released, shows up in this category and the same file I uploaded can be downloaded to my local storage. To be honest, I'm not even sure what "matched" means here.
Edit: Well... Now I'm even more confused. When I download
some tracks with Cloud Status "Matched", I get a proper local m4a file that I can open for example in an audio editor. I do think it has been replaced, though, as I get an m4a file that I'm pretty certain originally was an mp3 that I uploaded. However, other tracks with the same status, I get a file inside an Apple Music folder in my Media folder instead, with file type "HLS Media" (HTTP Live Streaming).
So I guess files are in fact replaced after all, I have just never noticed it. 🤔
Thanks for asking about this, now I need to rethink how I manage local files and make sure I actually keep stuff locally after it has been uploaded.