The lawyer who got Prince out of his contract with Warner Brothers was still his friend until today (and still his lawyer, I believe), so I would imagine all the work Prince did was being dealt with his lawyer so that the problems he experienced in the first part of his career were not repeated. So I imagine now that Prince's estate owns everything that Prince ever recorded. I would guess that anyone who recorded with Prince agreed to let him have the rights to whatever they produced. Or maybe joint ownership between Prince and that artist.
Prince has released an album a year since he left Warner Brothers. And some of those albums were double or even triple albums. Plus he released music under various band names as well. So it might be a matter or whether Prince
wanted any of that unreleased music to ever be for public consumption. That might be in the hands of the estate now. As for other artists, well, that might make things interesting!

I'm not sure I knew that Prince and Raitt worked together. I would
love to hear whatever they did!!