Thanks for your advice, @stupidname and @reosarevok.
Yes, the ampersand seems a little misleading.
I have taken the liberty of adding a new artist. For the purpose of this release (and a bunch of others) it seems to me mentioning two or more artists as composer in one breath, so to speak, is necessary and legitimate, and not merely in the case of transcriptions and orchestrations. I feel a bit uneasy seeing one of my favourite pieces credited to W. A. Mozart even though Franz Xaver Süßmayr composed the bulk of it, and that Tomaso Albinoni's famous Adagio was mostly composed by Remo Giazotto. The latter ought to be credited in the same box as the former. I think that should be acknowledged on the release and not just under the rubric of works.
I expect that my approach will not be accepted, though, so I'll just await instructions on how these things are to be handled in the traditional way, and I'll then stick them instead.