In one scene Jay says that he and Silent Bob watched a movie by holding the tape up to the light. Cassette tape doesn't work like film. Holding the tape up to the light wouldn't show anything.
When Dante is watching the finished film that they supposedly made recently, it was clearly just playing footage from the first two Clerks movies. And there was footage of Becky mixed in there, but she obviously couldn't have been part of making the movie since her character had died before the events of this movie.
In the end credits, the town of Holmdel, New Jersey is incorrectly listed as "Homdel" New Jersey.