Other mistake: When the boys cause a mini tremor by blowing up the girls' base, the time at which it occurs is strange because when they do it, both Stan's parents are at home (even though they both have jobs), Ms. Choksondik and Mr. Mackey are at Choksondik's house getting it on (indicating that school is over) and the other teachers are still at the school.
Butters' Very Own Episode - S5-E14
Other mistake: When Butters is travelling down the river in his mom's car, the passenger door opens just before the car hits the rock.
Osama Bin Laden Has Farty Pants - S5-E9
Other mistake: When Stan goes to answer the door after telling his mother that the doorbell is ringing, he clips through Sharon's arm. (00:04:31)
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.
Bishop73