What data does Apple use to "Match?"

[randally]

I recently went through my music library using "MusicBrainz Picard"(MusicBrainz Picard) to make all my tags consistent and also retrieve good album art.

Yet, after I restart iCloud Music Library (I am an iTunes Match subscriber), I am getting "duplicate" albums with the little cloud symbol in the bottom right corner of the album art. Is there anyway to make sure the tags are matched, other than manually going through the tags?
I also tend to be much more detailed in my tags than Apple uses for iCloud Music.

Does anyone know what database Apple uses to tag iCloud music? They used to use Gracenote, but I have found it to be very laborious to use myself.

 

[Tartarus]

I have fixed all my database with MusicBrainz as well and when a song isn't recognized/matched by iTunes, I go to iTunes, search for the album the song belongs to and make sure the track#, the song title, album name and artist name is the same as in the song I have. If it isn't, I copy exactly how iTunes has it catalogued. And that works just fine for me.