Deliberate mistake: Winchester is listening on the radio to the 1951 Giants win the pennant. In the MASH series, Potter was supposed to have arrived 19 Sept. 1952, and Charles Winchester after Potter did. The Giants won the pennant during the previous year, not when Winchester was there. Also Potter, BJ and Winchester are present for New Years parties for '50-'51 and '51- '52 even though none of them arrived until late 1952.
Continuity mistake: When Maj. Winchester hears that the Giants won, he drops his baseball cap. A few shots later we see him lying on his back, clasping his cap in his hand.
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 ★