Other mistake: When Frank's with Margaret in her tent and she tells him that she thinks they should reevaluate their friendship, there's a Life Magazine lying on her bed which is dated over 15 years in the future - August 25, 1967, with "The other war in Vietnam" written on its cover.
Other mistake: After Klinger gives the long johns to Mulcahy, he "disappears." But if you look closely through the camo net, you can see him in the shadows of the background.
Continuity mistake: When Henry is put on the table, he rolls onto his back while requesting gas. After a cut to Hawkeye, he's on his stomach.
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 ★