Looking at musicbrainz documentation re VorbisComment tags used by Picard and SongKong documentation regarding the same it looks like some tag names differ between the two meaning that a tag written by one won’t always be seen as already being present by the other. Is this the case or am I mistaken?
Tag name alignment with Musicbrainz Picard
We do try our best to keep them the same but there are a few minor variations.