Early 1983 at home, written while Vanity was on the tour
Basic tracking for Wonderful Ass sits in the first two weeks of January 1983 at Kiowa Trail in Chanhassen. November 1982 is still on the table if the tape log is read the other way. Prince played the instruments. Jill Jones was in the room and helped him land the chain of rhymes that end in “ate”. The usual account says the subject was Vanity, Denise Matthews, who was opening the 1999 tour while he wrote. The track is a Linn drum, a synth bass, and a vocal that keeps grinning.
Nobody has pinned it to a finished album. In 1983 there was talk of handing it to Vanity 6, then to Apollonia 6 after Vanity left, or to the Time. The Time idea fits the ending better than Purple Rain does. The last line is Prince doing Morris Day. It is a sketch as much as a song, the kind of gag those side-project records were built to hold, except he never gave the tape away.
Wendy Melvoin and Lisa Coleman came back to it at Sunset Sound, most likely on 27 September 1984, and added vocals, guitar and keyboards. The liner notes on the later Purple Rain deluxe date the whole track to that September. That date only covers their overdubs, not the home recording. On 28 March 1986 he edited it again at Sunset Sound, long enough that a B-side was discussed. It still did not come out.
You know I like that ass.
(Prince, closing tag on Wonderful Ass, 1983)

The song stayed down through the Revolution years. It turned up on a late-1990s compilation plan sometimes called Roadhouse Garden, still unreleased then. A snippet circulated. The full track waited until the Purple Rain deluxe editions in 2017, on the disc of vault songs. That release is a delivery. The session is a home date at the end of the 1999 touring year, a joke lyric tightened with Jill Jones, and a Morris Day sign-off he kept for himself.
What you hear is the 1983 track with the 1984 Wendy and Lisa parts, not a new arrangement built for the reissue. Prince is still the only producer credit. The rhyme game at the end is the tell. He was writing fast, in the house, between shows, and he left the tape funny on purpose. Purple Rain the album, finished the next summer, did not find a slot for it. The explicit number on that record went to Darling Nikki. This one stayed a studio joke with a real groove: Linn on the bottom, Jill Jones’s rhyme list in the last verse, and a Morris Day voice he could have handed to the Time and did not. Jones helped build the rhyme chain. She is not listed as a singer on the finished mix.