Revealing mistake: Just before the end credits, as Superman is flying past Metropolis and into space, watch the car headlights in the background. The background shot is blatantly sped-up by a large amount, as all of the cars appear to be travelling at huge speeds, even in a traffic jam.
Revealing mistake: During the airplane mishap where Lois is pinned to the ceiling, notice how the force is strong enough to hold her there, but both her hair and ID badge still hang down. (00:38:25)
Revealing mistake: At the baseball field, when Clark is holding the plane's nose he is replaced by an obvious CGI figure with zero facial expression.
Answer: The film doesn't take place between II and III, it just carries on from Superman II, ignoring 3 and 4 completely. Think of it as a parallel timeline.
Tailkinker ★