Other mistake: The FBI agents call for a taxi and official transportation from the Evans apartment and gave the address of 963 North Gilbert. However, the Evans lived at 921 North Gilbert. Since the FBI was at their apartment, you would think that they would know the address or exactly where they are in a Chicago project. (00:13:03 - 00:28:29)
Other mistake: Vincenzo is looking at a photo of the gorilla Kolchak took of it earlier in the episode. It is a side shot, but Kolchak took two pics when he encountered it, one frontal, and the other shot as the creature was running away from Kolchak and the authorities.
Other mistake: The background action in the opening credits is slightly unsynchronized. This is most obvious at the "Goodbye gray sky, hello blue" line in the theme song, as Potsie mouths the lyrics. It's also obvious at the "My cycle hums" line, as the girl in the blue plaid skirt shows up at "cycle", rather than "my." (01:13:10)