During one scene in Col. Potter's office, Col. Potter is spelling someone's name on the telephone. Hawkeye, standing nearby, responds by chanting "M-O-U-S-E" - part of the "Mickey Mouse Club" show's theme song. The "Mickey Mouse Club" did not debut on television until October 3, 1955, more than two years after the ceasefire that ended the fighting in Korea.
Throughout the series, Margaret has very long fingernails. As both a nurse and a Regular US Army officer who's a sticker for the rules, there's no way her nails would be so UN-regulation. Neither nurses nor Army officers have long fingernails.
BJ's daughter Erin's age is constantly jumping back and forth. When he first arrives, he explains that he received his orders to report after returning home with his wife from their first night out after Erin was born. When Radar leaves, Erin is big enough to walk up to Radar and call him "Daddy." In the next season, BJ explains that on his last anniversary, Peg was still 8 months pregnant with Erin, which would make her less than 1 year old. A few episodes later, Erin is once again talking in full sentences and is nearly 2 years old.
In Harry Morgan's first season as Colonel Potter his only child is a son whose wife has a daughter. However, by the end of the series his only child has become a daughter and her husband visits Col Potter at the 4077.
Hawkeye's background and family situation changes quite a bit during the run of the series. At the beginning he is from Vermont, both parents are living, he has a married sister that sends him an oversized homemade sweater, and a nephew. By the end of the show, he is from Crabapple Cove, Maine, and he is an only child whose mother died when he was about 10.
Several of the characters had multiple variations on their names during the series, perhaps none more so than Father Mulcahy. His name is given at various points as John, John P., Francis, Francis John Patrick, and John Patrick Francis
Although the Korean war lasted slightly over than three years (Summer of 1950 through Summer of 1953), MASH seemed to pack at least four or five Christmases throughout its run. Of specific note: Dear Dad - 1972, Dear Sis - 1978, Death Takes a Holiday - 1980, Twas the Day After Christmas - 1981.
Throughout the entire series, the nurses referred to as "Baker" have been different women, including one (in contrast) black woman, some (in contrast) single women, and a married one, whose husband Tony spends the night with her in Hotlips' tent.
In the early seasons, Vietnam-like references were often made by characters: Claiming their location was in "Southeast Asia" (Korea is in northeastern Asia) and searching for missing colleagues in "the jungle" (there are no jungle regions in Korea).
As a rule in the service, a person is only awarded one Purple Heart (the first time they're wounded) and then oak leaf clusters for subsequent injuries. However, multiple characters throughout the series have or receive more than one purple heart.
In several episodes, Radar misinforms another character about the time difference between Korea and the United States. During one attempt to call a stock broker in New York City, Radar tells Maj. Burns there is an 18-hour time difference. The time difference between Korea and New York is 14 hours during standard time months and 13 hours during US daylight savings time.
Three different people have been named "Nurse Baker", including a single woman, a married woman and a woman of a different race (she was Black while the other two were Caucasian). However, Baker is a popular American name, and could have been shared by more than one person in the 501st. In addition, "Baker" is the second entry in the old US Navy radio alphabet. "Able," the first entry, is the name of several nurses throughout the series. "Able" and "Baker" appear to be placeholder-type names, possibly an in-joke for military viewers.
Two sets of the camp were built, one in the outdoors, and one within a studio. This is apparent in numerous episodes when the characters are standing "outside" in broad daylight, but each cast member has numerous shadows as a result of studio lights shining in different directions, as well as an echo within the studio that is not audible on the outdoor set.