So I've tried this option numerous times in Picard with no luck. Right click a track or album, select "Add New Tag," write in the tag field and edit the value. After doing this the tag never actually shows up.
Basically, if a given tag field wasn't present when Picard looked up the album (for example, missing record label info) there is no way for me to add it in Picard. Or if, say, I want to add something in the comment field, I can't, because a "comment" tag would never be present in an initial MusicBrainz lookup. I'm stuck using some other program just to enter that one tag, very annoying.
Is there something obvious I'm missing here? The option seems like it should be very straightforward.