Visible crew/equipment: When Klinger's at Little Chicago he asks one of the black market vendors about cameras and he points to another vendor, and when it cuts to the next shot we can see the actor's T-mark on the ground where the man walks away (his foot even moves the T-mark) and Klinger is about to stand.
Continuity mistake: When Klinger's stopped by the MPs it cuts to a close-up of the Polaroid camera and it's lying between the seats with its hand strap facing the front of the jeep, but when Klinger picks it up the camera's positioned the opposite way with its hand strap facing the back of the jeep.
Answer: The C-42 was a military variant of the Douglas DC-2. Very few C-42's were built, so it's questionable that Potter would specifically have seen that particular model, but, given his military background, it's not entirely unreasonable that he might use the military designation even when the aircraft in question is actually a civilian DC-2.
Tailkinker ★