I remember watching a clip on youtube a few years ago of Kevin Smith talking about getting invited to Paisley Park to shoot something for Prince. He mentioned that Prince's assistant told him that Prince has a vault with thousands of unreleased songs - & many have had an accompanying video as well. When Smith asked when they would be released, she told him maybe never.
It's been a couple years since I've watched it (video below) so my memory may be a little off but it's worth watching if you have some time to kill & don't mind Kevin Smith.