Factual error: The gang keeps referring to the theme park 'Great America' as "Six Flags." Up until the 80's the park was actually Marriott's Great America. There is no other Six Flags theme park in the area. - from Wikipedia "Marriott Corporation began construction on the park in 1974, and opened it in 1976 as "Marriott's Great America". In 1984, the park was purchased by Six Flags Corporation, becoming the 7th Six Flags park."
Factual error: Episode 7-2, "Let's Spend the Night Together" After Kelso gets the call that his girlfriend's water had broken and runs out of the room, Fez answers the phone. In the background there are several license plates on the wall, one of which is an Indiana "Amber Waves of Grain" design, which was first issued in 1993.
Factual error: When Donna and Randy are in Eric's bedroom, Randy is playing with Eric's toy lightsaber. However, the blade is green. No green lightsaber toys were produced until after the release of "Return of the Jedi", which occurred in 1983. Moreover, the handle is the modern style, not the vintage.
Continuity mistake: At the end of the episode "You Shook Me", Jackie is talking to a drunk Kitty who is putting mini umbrellas in Jackie's hair. The first shot of her doing this, she puts a green umbrella on the right side of Jackie's head. After Kitty asks for more umbrellas, the shot changes to Jackie which now has a pinkish, red umbrella on the right side and two green ones on the top.
Factual error: During the episode, it goes back to 1968 and in the closing credits Eric is listed as being 7. However, he can't be because in 'Eric's Birthday' it was 1976 and he had turned 17. Thus in '68 he would have had to be 8 or 9 (depending on his birth) but certainly not 7.