There are often release dates in MusicBrainz which are not exactly the same day as the “official” release dates.
I know the different release dates in different countries, often in the past. E.g. in UK it was one day before in real Europe.
Often you can’t find a reliable source for the release dates. Sometimes it is on Discogs and you can’t find a reference there.
Some [types] of my files have the original release date just as year (as it was the default supported format of Picard [for some metadata types] in the past or a consequence of a different sorting method for the first release date [i.e. year-only before full date]). Since the full date format is the default format in Picard many of my files have differences.
Not all first release dates in MusicBrainz are the real and official release dates (and not all release groups have the initial release).
One example for a first release date one day off is Herzeleid by Rammstein:
The official release date is 1995-09-25 on the website of the band, on the nice retro-page for the 25th anniversary and on Wikipedia (publication date; de and en site).
In MB one release has the 24th (for Europe), based on Discogs.
I’m not sure if the 24th is wrong at all, since it might be a possible release date e.g. in the UK.
I don’t like to have a non-official original release date. In this case I’m happier with just having the year in such cases. If the date is correct I’m happy to have the full date. Also if there are more than one releases in one year the full date is very helpful.
Sadly there is no official release date but just the first release date. For me it would be fine to have an official release date (for the release group).
P.S.: I know, it is not always clear what the official release date is. Often you can’t find it (easily). However, if a release date is used on the artist’s page and/or by the label I’ll call it “official”.