I think much or all of the metadata ends up in the Gracenote database (and probably others) based on whoever first popped the cd into some application and updated the database.  For example sometimes when I have gotten a very recent Mosaic set, the metadata was not set up in applications like iTunes and I had to enter it myself.  

Just arrived from Japan and I had to put it into the transport. . . . “John Coltrane Quartet Plays” Impulse/Universal Japan SHM-SACD  

IIRC, at least some of those Honeydew Elvin albums had exceedingly long drum solos, which made them hard listens for me, even though I'm a big fan of his leader work in general.

Now on to this classic, in mono form. Herbie Hancock “Maiden Voyage” Blue Note Japan Platinum SHM-CD     And then   More mono, this time re-listening to disc 4 of this great new Mosaic set.   300×300 17.8 KB   Classic Decca Recordings Of Bob Crosby And His Orchestra & The Bob Cats (1936-1942) It’s interesting that this band grew out of the Ben Pollack band, a band I’ve always enjoyed.

I don't think one can hold Mosaic responsible for the "tagging" of the digital files uploaded.