Prince was an artist well known for recording on a whim, and recording a lot. Many people who have visited Prince's home and studio, Paisley Park, have said every room is wired to record and Prince is known to have a guitar strapped around himself so if he gets an ides he could record it. A former engineer of Prince's claims he has music from Prince that he has permission to release. 

Prince's estate put the kibosh on that transaction. At first you could listen to one of the tracks on iTunes, but that has since been taken down. According to Business Insider, Prince's estate sued George Ian Boxill, the engineer and co-producer of the music, who claimed he had rights to the music. The Prince estate was granted a restraining order that only lasts till May 6th. Now, both sides will have time to prepare their arguments, but Prince's side looks strong. Their argument is that every engineer and producer Prince works with have to sign papers saying Prince owns everything they do.

Until that time, Warner Bros. Records plans to release an anniversary edition of Purple Rain which will include 3 discs of remixes and movie music.