Prince had an actual, physical vault at his house, i.e., a climate-controlled room with an alarm system and a secure door. After recording, whether it's a song or film reels of a concert, it would all go in there:
Michael left things at studios (after he died, some unreleased music was found at recording studios such as Marvin's Room in LA) or with people who worked on them (video material, multitrack recordings) from musicians to studio support staff. He didn't catalog or organize much of anything in his life. If he needed something, he would usually have someone hunt it down for him. He seemed to be quite messy and disorganized even when living at Neverland:
The fact that he moved from house to house in the final years of his life didn't help.
