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.