Simpsons Already Did It - S6-E7
Character mistake: Butters says that he watched "all 132 episodes" of the Simpsons; at the time this episode aired, 291 episodes of the Simpsons had been produced and aired.
South Park (1997)
1 character mistake in season 6
Starring: Trey Parker, Isaac Hayes, Matt Stone, Mona Marshall
Woodland Critter Christmas - S8-E14
Continuity mistake: The narrator says that it's "Christmas Eve day," but then the abortion doctor says that it's "three days until Christmas."
Cartman Gets an Anal Probe - S1-E2
Cartman: How come everything today has involved things either coming in or going out of my ass?
Question: Forgot the episode and the season, but does Mark, the kid that gets home schooled and ends up beating Kyle, ever show up in later episodes?
Answer: He appears in at least 5 other episodes, but usually just as a background character. He can be seen at Cartman's party in "Immaginationland". He was also one of the kids trying out to replace Butters in the "Professor Chaos" episode.
Suggested correction: Butters is always shown as being a bit dim and slow. As a kid it's easy for him to make a mistake in thinking that there was only 132 episodes.
Ssiscool ★
That's why it's called a "character mistake"; also, Butters is certainly naive, but he's hardly what I would call "dim and slow."
zendaddy621