There seems to be no way to include tracks in an album that are not part of the standard list of tracks without making them be tagged with the wrong track specific tags.

I sometimes have albums that have audio that is not a normal track, like Track 0 audio, or audio files from a data track.  I want to keep these associated with the album, and tagged with the whole-album tags, but if I drop them on the album, Picard ends up stuffing them into one of the other tracks as a duplicate even though it doesn't match at all, and I can't seem to find a way to disassociate it from any of the "known" tracks without also completely removing it from the album.

I think there should be an item on the track right-click context menu to "Keep with album but mark as unmatched" that will move the track out of the track it is associated with and to the "Unmatched files" section of that album.  Then if the album is saved, it should tag any files in the "Unmatched files" section with any tags that apply to the whole album, but NOT modify or set any track-specific tags.  It should also keep that file with the rest of the tracks if the save moves them to a different location, so that they don't get disassociated with the album.