Scotty says that the film John and Chris shot of Daniela in 1979 was an 8MM film, and indeed, it is a black and white 8MM film. But in the flashback, when John and Chris are filming the snuff reel, they are using a super 8 camera to film it. Super 8 is different than 8MM film and the two are not compatible with one another.
Prom set in May 1979, the song Please Don't Go by KC and the Sunshine Band is played, which was not released until July.
The song "My Sharona" by The Knack is heard in a 1979 scene (before the prom in May); it was released in June.
Supposedly it's supposed to be March 15, 1979. "Bad Girls" by Donna Summer is playing. However, the album Bad Girls was released April 25, 1979. The song was released as a single June 23, 1979.