Those probably already have MBID's attached, so they automatically get "shoved" right if you have that option enabled. If you want to "sanity check" your whole collection just to give it a try, you could temporarily set the option "ignore MBID tags when adding new files" and run a scan on it, to see what would change (just make a backup or be very careful not to safe anything ).
To clarify: I don't mean red release icons - those are just error messages (like p.E.: "couldn't load album art from X"). I meant the red tinted recordings: The more tags would get changed, the stronger the red tint of that recording is. This is why I use acoustid / scan initially. Most of the slightly reddish tinted recordings will just be updated data (year, accents added, featured artist updated etc), but then there's some that will be deep red, because the tags from the fingerprint match are totally different from how it was tagged before:
(problems with the files: )
- File has (initially) been tagged VERY incorrectly
- Tracks have been switched around somehow
- Recording is actually from different artist / cover version
- File is broken / contains silence from a ghost track and bonus track that shouldn't be there for the release it was tagged as
or (Problems with musicbrainz DB):
- Someone added an acoustid to the wrong recording
- The acoustid has simply been added to the same recording from a different release group (p.E. compilation), in which case the information attached to your files was right but sometimes it might make sense to merge recordings online if noone already has.
How often you get those depends mainly on where you get your music from. If it's a competent & trustworthy source, the files have been tagged well before and you focus on complete / whole albums from widely known artists, you might not discover anything useful except that "those files are probably really in good shape!".
If on the other hand you get "mixtapes" from random people sometimes or something like that, this could help detect a lot of mis-identified recordings.
Either way - it doesn't usually take long since I can just "expand all" + scroll through it, then drag it all back if there's no problem. I'd guess when I first add files, for every ~300 files from ~100 different artists, I find about 1 "terrible mixup" (totally wrong release + band + title) that way that I wouldn't have had a chance to catch - ever - otherwise... and that alone makes it worth that extra step in my case.
Just scanned some of my existing files again just to see if the acoustids that have been submitted since I last checked changed anything. In ~2000 files from ~1000 releases that have already been checked several times before, I found:
- 7 recordings that were tagged as the correct work but wrong recording (/ mostly different intros/outros, radio version etc : same release group but release from a different country and something was bleeped etc)...
- 1 that was a cover / "reinterpretation" from an entirely different (less known) artist than what the tags said...
- 2 where my tags were correct but someone else seems to have submitted the acoustid from a wrong track (have yet to figure out how to report that)...
- 1 that was recognized as an obscure live bootleg by "lookup" somehow when really it was just the (non-live) "album version" from a compilation (no idea how that slipped by me - had that file for years)...
- 1 file where the last few seconds were simply missing and I thought it was supposed to end that abruptly :D...
- several recordings that should be dupes in the MB DB (have yet to figure out which ones should be merged)
- and more small stuff.