Continuity mistake: When Radar goes to get the lamb, he pulls out a hypo to put the lamb to sleep for shipping. When the shot cuts to the lamb, you can see both of Radar's hands on the lamb's face; no hypo in sight.
Revealing mistake: The sound of crew making an explosion with their mouth as a cue can be heard just before the actual audio of an explosion plays.
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 ★