In Harry Morgan's first season as Colonel Potter his only child is a son whose wife has a daughter. Later on he has a grandson named Cory who went from a newborn to being a five year old. 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.
Colonel Potter enters the series as a Methodist and is a Presbyterian just after Radar goes home.
In one of the early episodes, Henry Blake refers to his wife as "Mildred". However, in later episodes her name is Lorraine. Col. Potter's wife's name is Mildred.
In early episodes, Margaret's father is deceased. However, later in the series her father "Howitzer Al Houlihan" actually visits the 4077.
Franks Burns and Hot Lips Houlihan's affair would have been far more scandalous in the 1950s setting of the series than in the 1970s/1980s airing. Since Burns was a married man, violations of military law would have been an issue and the affair would have quickly ended or resulted in both being removed from the service.
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.
Very few of the actors are the right age for their characters. Hawkeye, Trapper and BJ are supposed to be just out of residency, yet all were portrayed by actors in their mid-30s or older. Max Klinger was portrayed by Jaime Farr, in his late 30s, but a draftee would've been 18-21 or so.
Some of the nurses are seen with long sculptured nails. Nurses who work in operating rooms don't wear those kind of nails.
Several subplots revolve around the search for AB blood. Type AB is known as the universal recipient. As long as the Rh factor is negative, any blood type will do in an emergency.
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.
Powerlines are visible in the background of some exterior shots.
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.
Although done throughout the series for comic effect, Hawkeye's insubordination would have very rapidly landed him in a general courts martial and the stockade.
In the opening credits, the helicopters are shown flying backwards as the title of the series appears onscreen.
Throughout the series, Douglas MacArthur is referred to as though he is still in command of the UN forces in Korea. However, MacArthur was relieved of command by President Truman about ten months into the war; April 11, 1951 to be exact.
Radar is seen reading Marvel Comics that were actually published in the mid-1960s.
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.
In Colonel Blake's office you can see a model of an UH-1 "Huey" helicopter hanging from the ceiling. However, this type first flew in 1956, years after the Korean War came to an end.
Velcro used on the blood pressure monitors. Velcro was patented in 1955.
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).
The 4077 has a travel directions sign. The signs for Tokyo, Boston, and San Francisco, which are all east of Korea, are pointing in different directions. There are also two signs for Seoul which point in opposite directions.
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.
There are various episodes with Korean nationals such as farmers, villagers. These Koreans speak English. It is highly unlikely that the native Koreans would speak or understand any English especially in small villages away from a city.
On various occasions, the War Department is mentioned by various characters. This is in error as the War Department was renamed the Department of the Army in 1947. When referring to directives from Washington D.C., they should use that title or it's parent organization, the Department of Defense.
Several characters change blood type during the show.
In the Army, caps (cover) are always worn outdoors and never worn indoors.