In an early episode of mash, Hawkeye has a sister who knits him a sweater. Later on he will say on a number of occasions that he is an only child. What happened to his sister.
Writers it seems feel that audiences generally have bad memories. If you are a MASH fanatic like I am you notice all this stuff. Even if you're not, some things don't get overlooked. For what it is worth, however, the writers of that period were better than the ones today.
You should also remember that in the early days of M*A*S*H things were still new, such as the characters backgrounds. As the show moved on it got more serious in its content. True M*A*S*H fans know that some episodes were edited even further as they reran the episodes later in the 1990s.
I guess whoever submitted this "slip-up" must have lied on the page before posting, because it says DO NOT POST DISCREPANCIES BETWEEN EPISODES OF A SERIES.
If you recall, Hawkeye has had a sister, a mother, and has lived in Vermont. All of these things happened in the early episodes. After that, he has been an only child with a widowed father and lives in Crabapple Cove, Maine.
But, even so, this is not a slip-up.
Hawkeye ain't the only one with a flawed family tree. "Hot Lips" Houlihan also has a questionable history. Very early episodes have her mentioning that her father was no longer living, and that she was responsible for caring for her alcoholic/kleptomaniac mother. But a much later episode featured her dad, "Howitzer" Al Houlihan visiting the 4077th. Did he come back from the dead?
As someone else mentioned in the earlier episodes they had several goof ups in one he said give my love to mom and sis yet even in the movie he said his mother was dead. Also there are several goof ups when it comes to the movie versus the show.