Something that is “sold together” doesn’t necessarily mean it’s a single MusicBrainz release. You’d typically expect a MusicBrainz release to have been originally packaged together, not just “sold together”. If you take a product off the shelf, take it to the register, and the clerk gives you a separate gift, that’s clearly two separate MusicBrainz releases to me.
That’s how we used to deal with Japanese releases from labels infamous for doing this, like EXIT TUNES.