I actually did own a Poison album -- on cassette -- in the 1980s. I probably didn't find out about Aimee Mann until Magnolia in 1999, like much of the rest of America. Though I did have the Jerry Maguire soundtrack, which included "Wise Up," three years before that.
When I interviewed Aimee in January, I asked her to clear that up:
ME: You’ve introduced the song “Wise Up” a few times as “a song from Magnolia,” a film which of course made prominent use of, and was in part inspired by, your music. But “Wise Up” was on the Jerry Maguire soundtrack three years before Magnolia came out. Were you making a point by associating it with the later film?
MANN: Well, I wrote it for Jerry Maguire. [Writer/director Cameron Crowe] really liked the demo, and then he didn’t like the finished version, so he didn’t put it in the movie. Then after the movie came out, he called me and said, “I don’t know what I was thinking! Your version is awesome. I guess I was just kind of attached to the demo.” So he put it on the soundtrack album. So it’s there, and on the DVD, but it wasn’t in the original release of the film.
And then [Magnolia writer/director Paul Thomas Anderson] heard it, and he really liked it. So [the song’s prominent use in Magnolia, a surreal sequence wherein several characters in different locations are seen simultaneously singing the tune aloud] was kind of a sweet shout-out.
In any case, time and maturing taste has made my allegiances clear.