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.
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: When Flagg turns out the light to escape.To make that effect they had to freeze a frame and then start again. If you look closely after Flagg turns out the light you can see Hawkeye and the Korean Man on the far right freeze. Then it shows Potter ordering the light back on.
Deliberate mistake: With the show having lasted longer than the war, the producers apparently decided to turn back the clock to the very beginning of the War (June 25, 1950). To do this, it seems they have tried to make things as confusing as possible, intentionally mixing up facts, even when this openly contradicts the facts as presented in earlier episodes. For example, both B.J. and Potter arrived in or about mid 1952, but now are in the O.R. when the Chinese launch their massive offensive on 1st Nov. 1950, almost two years earlier. Trapper and Blake, who were there for the Army Navy Game which would have occurred Nov. 25 1950, are not. Many of the supporting clips also are too early or late for the events being discussed. For example, Winston Churchill's speech must have been before August 28 when the first British troops started arriving, likely also before the Canadians in July 1950, but the first MASH Unit was not set up in Korea until September 1950. Truman's speech to University of Wyoming students is actually from May 9 1950, a month and a half before the beginning of the conflict and 5 months before the first MASH was established, but the clip about his "Whistle Stop Tour" must be from the 1948 campaign. MacArthur's speech, on the other hand, is in response to the ticker tape parade of April 22 1951 when he was replaced.
Deliberate mistake: BJ mentions to Charles that if they don't sign the armistice it will be the second time in 2 years and then he will miss his daughter Erin's second birthday. This is BJs 7th season and when he arrived at the beginning of season 4, Erin was already born, making it absurd that seven years later she could still be one year old. Because the real war lasted 3 years and the show 11, there are obviously some errors like this that can't be avoided but this was blatantly egregious.