Other mistake: Sammy makes his film "Escape to Nowhere" with a Bolex 16mm camera. (I recognise it because I own one.) When he shows the film, we can see that it is on 8mm film.
Continuity mistake: When Sammy tells Boris, he has to make the camp movie, he holds the script with one or two hands depending on the angle.
Mitzi Fabelman: Everything happens for a reason.