I don’t know much about this, but often when I add a (rather obscure, admittedly) release to MusicBrainz, I have to upload cover art as well (which I then usually manually take from Amazon or Discogs).
So my guess would be that the CoverArtArchive doesn’t always help. Or is the cover art I upload to MB automatically fed back to CAA as well?
I had the situation however that the cover art that was fetched / embedded by beets is not identical to the one that MB Picard embeds. And at least in that case the MB Picard cover art was the correct one (for that release in MB).
So the fetchart plugin using coverart source doesn’t produce the desired results, which is fetching the cover art associated with the musicbrainz release in musicbrainz.
Or does it take more than a day for the cover art to be synced from musicbrainz to the coverartarchive?
Did you have the Cover Art Archive listed as the first source in the beets configuration?
Here’s my config:
fetchart:
sources: itunes filesystem # fanarttv coverart albumart amazon wikipedia google
If I place coverart at the beginning, fetchart grabs the correct cover. I suppose that the image chosen by beets may also depend on its place in MusicBrainz or the tag assigned to it (front, spine, back, etc.).