Deliberate mistake: These errors I assume were caused by the show running 3 times longer than the real war. Col. Potter arrived at MASH in September 1952 a year before the war ended, then a few months passed by Margaret got engaged for 8 months, then Frank Burns left and Charles took his place. In this time the war would have ended. In the final episode Margaret mentions Charles has been there for 2 years. Which means he would have arrived in 1951 a year before Trapper and Henry left and Col. Potter arrived. It's a lot to take in.
Deliberate mistake: The circular desk where Carol sits should be rotated 180 degrees so she is facing the elevators. How many times have you gotten off an elevator in a fancy office building only to see the back of the receptionist's head?