MASH is one of my favorite shows, however it is completely ugly with errors.
Dates in time go back and forth. For example, Potter reported for duty in September of 1952, however in an episode several seasons later, the unit had their own mock olympics to commemerate the Summer games which would of occured BEFORE Potter's arrival to the unit.
In the series there were four Christmas episodes, even though the Korean War lasted only three years.
On one episode, they showed Hershey Bars with UPC codes on the back.
The shoes that B.J. wore were from the 1970's.
The pinball machine in the Officers Club did not come out until 1960.
There is a red sign of a medical helicopter unit, which was a real sign from the war, the Vietnam War. Whoops.
On movie night, they showed Godzilla, a movie that came out several years after the Korean War.
Radar's comic books were made after the Korean War. (like in the 1960's)
Hawkeye was originally from Vermont with a sister and parents back home. By the end, there was no sister, the mother died when Hawk was a child and it was merely him and his father, now living in Maine.
Potter's horse at first was a male (the episode where he was given the horse) which changed to a mare.
Potter claimed that Harry S Truman was his commanding officer in WWI even though Truman was in the artillery and Potter was in the infantry, and were from opposite ends of the state of Missouri.
Potter once said that he had a home in Nebraska, which was changed later (for some reason) to Hannibal Missouri. He also said he was a Prespyrterian which was changed (for some reason) to a Methodist.
Hawkeye basically stayed in the same unit for the whole three years which would not happen in real life. Basically a real Army surgeon would get rotated home or another post in months or less.
In Sidney Freedman's first appearance, his name was Milton.
Blake's wife's name was Mildred, later called Lorraine. Potter's wife was then called Mildred.
Father Mulcahey's middle name was changed from Patrick to Francis.
Certain actors were in 1970's mode. Loretta Swit and that huge Loni Anderson hair. Mike Farrell (B.J.'s) cheesy mustache and goofy hat. Almost no men in the service wore mustaches during that period, and especially nothing like that. Not to mention that crazy hat of his.
While waiting for Major Burns (the first episode with David Ogden Stiers, aka Winchester) Potter offers Radar a cigar, in which Radar claims to have never smoked before. He must have forgotten that he used to drink Blake's brandy and smoke his cigars back in Season one (Chief Surgeon Who?). Unlike a lot of the other goofs, the writers wanted to change Radar's character. At first Radar was going to be a bit of a streetwise person and somewhat of a sneak, and the writers that this was bad and basically redeveloped the character's overall personality.
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I think that there were so many continuity errors is that the show had different writers and the mood and tone of the show changed over time. Also, this was the 1970's and early 1980's before the advent of the internet. Some prop person finds an old pinball machine somewhere and thought it would look good and doesn't know the age of what he has. Other things like Godzilla and the UPC codes were somewhat inexcusable.