Young Bart is handed the U2 album The Joshua Tree (1987) in 1985.
When Bart's mom is driving him to the camp, and Bart puts in U2's The Joshua Tree cassette tape. Then a U2 song starts to play , but the song isn't from The Joshua Tree, instead the song is" Into the Heart" which is a song from their first album Boy.
In the 1985 scenes, the record store has a poster in the window for the first .38 Special record. This album came out in 1977, and was not a big commercial success at its time of release; its popularity was eclipsed by the band's subsequent releases. Additionally, it was already horribly out of date by the time this scene is set; no record store would be likely to display a poster for an album eight years old that was not commercially successful.
Bart tells his Dad that he will be singing at the church and he can listen on AM 1080. Every scene in the movie that shows his Dad's radio shows the band switch in the FM position, not the AM band.
The version of "Hallelujah" the Glee club was singing in 1991 is based on Jeff Buckley's 1994 rendition.