Most certainly covered, but I couldn’t find an answer or discussion.
In the video “How to Work With Divisi in Dorico Pro” it is said (copied from Of note’s transcription):
When you edit an existing divisi in a way that removes some of the staves you have previously been using, Dorico does not delete the music. You can think of it as the staves still being in existence, you’re just not using them at the moment. This mean that if you then bring back those staves in some way, the music will still be there.
It also means that any music left on divisi staves that are removed will still play back, so you may want to delete music before removing a divisi event.
I’ve deleted divisi staves without deleting their music first. Is there a solution to delete the music completely, so it doesn’t play back?
Moments later …
Found it. The music reappears when re-creating any divisi staves, then I can delete the music and then the staves themselves.