I have an album which was released on 12" vinyl and digital: “Mass:Light” by Murray Lightburn. Release group is https://musicbrainz.org/release-group/f92079e4-b698-4fb7-ad7f-f9dbba98659c.
I bought the vinyl release (https://musicbrainz.org/release/c49ec712-8661-458c-b78b-69e25ad2790d) and used a download code to download the digital release (.zip file of MP3s). At the time, I was able to download an additional .zip file with more MP3s; the tags on those files say the album name is “Mass:Light (Bonus Album)”. I didn’t pay any extra for this bonus album; both downloads were covered by the same download code.
The “bonus album” does not exist in MusicBrainz at the moment, and I’m not sure how to add it. To me, it seems extremely similar to buying a CD with some bonus tracks on it, or with a whole bonus CD in the same package. I bought an album with 9 tracks and the artist/label threw in 5 more tracks “for free”.
My inclination: add a new medium (digital, 5 tracks) to https://musicbrainz.org/release/c49ec712-8661-458c-b78b-69e25ad2790d.
Does this seem reasonable?