Continuity mistake: Phoebe is going into the school in one scene, but as the camera moves she vanishes while on screen.
Continuity mistake: At the start, Lila is sitting on a bench near the school wall. However, in the shot where Sheena says, "Oh, that's wonderful," Lila and the bench are missing; then they reappear a moment later. (00:01:13)
Character mistake: The first time Arnold tries Rhonda's marriage predictor test, he says his favorite number is five, but Rhonda actually makes six moves. The second time, Arnold says it's three, but Rhonda counts off four.
Continuity mistake: When Rhonda asks Lila if she wants to take the marriage predictor test, Lila is holding three books, but she is only holding one book in the next shot. (00:01:42)
Continuity mistake: When Pea Pod Kid is taking Rhonda's marriage predictor test, Sid is walking down the stairs behind them. In the next shot, he disappears. (00:03:44)
Revealing mistake: In Arnold's nightmare, when Bob points out that a stork is flying off their roof, his legs are incorrectly layered behind his cape. (00:12:50)
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.