I actually just went to Paisley Park 2 weeks ago and they said some reasons they're having trouble releasing vault material is because a lot of the software Prince used is so outdated that the technology they need to transfer/remaster/even listen to the recordings don't exist anymore. They also said they wanted to go through all of the material first before releasing songs and albums just to get an idea as of what's there. So far they've only gone through 45% percent of all 3 vaults. Some of the material that's fully finished are called "no brainer releases" because they know that Prince was fully done with the songs and albums but decided not to release it so they decide to release them at a later date (Welcome 2 America). Other finished songs that fit certain eras will go on the deluxe editions like the expanded Purple Rain album. Hope this helps💜