The musical “Buddy: The Buddy Holly Story (Original Hamburg Cast)” lists the original singers as the performers. But completely different performers sang in that production. Shouldn’t they be listed as the performers? What do you think?
and see booklet
The credits can be entered exactly as they appear in the booklet. If the performers, as you said, aren’t singing/playing on all tracks, they should generally be entered at the release level, except those assigned to specific tracks, e.g. Guitars on No. 4 - Uli Kringler.