Right now, a release is linked with its label (or labels). However, the catalogue number and format is not given.
If we add this information, it will mean a new compound value type, since the catalogue number has to be associated with the label and format. See MusicBrainz’s record for Sgt. Pepper’s Lonely Hearts Club Band for an example of how this would be modeled.
Is this too complex? Should a so-called “release” with multiple formats be forced to split into multiple releases? If so, what happens to the MusicBrainz-correlating IDs, since MusicBrainz is not so careful?