As a huge early-/mid-career Prince fan, this is a surprising take. Prince was famous for his meticulous attention to detail and perfectionism in the recording studio. The lore is that "Purple Rain" (the song) went through 91 mixes before Prince was satisfied.
"It’s really important. I think that’s a really important question. People have asked me, or they’ve prefaced questions by saying, “Prince was known to be a perfectionist.” I always have to correct them. He was not a perfectionist. He wouldn’t have had that output if he’s been a perfectionist. What he was was a virtuoso player and a genius with melody, a genius with rhythm, a genius at writing songs. It just poured out of him – he couldn’t wait on perfection. The important thing was to have the sound serve the ideas, not the other way around. Working quickly was fine with him and only a beginning engineer would have no bad habits to break. Only a beginner would be willing to go that fast."
If a perfectionist is concerned only with perfection at release time, then lots of imperfect unreleased material can exist. Prince is likely an example of this case.
If, on the other hand, perfectionism is applied to every step of the artistic process, then I'd reckon that very few imperfect unreleased materials are likely to exist. Steely Dan are a good example of this case.