Monkeyman! / Buses, Bikes and Subways - S5-E1
Revealing mistake: Monkeyman!: When Arnold tells the kids that Monkeyman saved him, as he says, "He went after the two guys who were trying to mug me," he moves his right hand, and it's layered over Helga's hair. (00:01:25)
Monkeyman! / Buses, Bikes and Subways - S5-E1
Revealing mistake: Buses, Bikes, and Subways: When Helga and Harold are riding the clown bike, a tall clown and two little clowns start chasing them. As the clowns are running, the left little clown is layered over the tall clown's right leg for a few frames, and the right little clown runs right through it. (00:17:39)
Answer: The show is based in present day times. Plus most cars aren't old fashtioned, I recall seeing a limo and not to mention a cherry picker, etc.