Gerald's Game / Fishing Trip - S5-E15
Other mistake: Gerald's Game: When Arnold is watching Gerald and the other boys play The King Rules through the window, as Gerald says, "Are you implying that I'm not going to be king forever?", his eyebrows duplicate as he blinks. (00:05:16)
On The Lam / Family Man - S5-E17
Other mistake: A security guard in the train yard is drinking from a carton of milk depicting the boys. However, they had only been declared missing that afternoon. It is impossible to put out milk cartons that quickly.
Simmons' Documentary / Big Bob's Crisis - S5-E20
Other mistake: Big Bob's Crisis: When Bob faints at the restaurant and first appears as an angel, his eyes become the same colour as his skin twice. (00:13:58)
Timberly Loves Arnold / Eugene, Eugene! - S5-E22
Other mistake: Timberly Loves Arnold: When Harold is leaving the field after the baseball game, he vanishes while on screen without fully leaving the frame. (00:06:15)
Timberly Loves Arnold / Eugene, Eugene! - S5-E22
Other mistake: Eugene, Eugene!: After Phoebe and Helga walk into the auditorium, the shot fades to inside the auditorium. If you look at Mr. Leichliter in this shot, you will see that his body is missing. As a result, his head and scarf are floating in mid-air. (00:11:50)
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.