When Eric is in the basement talking with Hyde, Fez and Jackie, Jackie's sun dress strap is off her shoulder in her closeups and on her shoulder in the distant shots.
Hyde's Ted Nugent t-shirt reads "Intensities In Ten Cities" on the back. This is the name of an album released in 1981.
When Kelso is wondering what they can do to kill a couple of hours, a background extra is wearing a Steve Miller Band "Lost Cities Tour" t-shirt. That tour took place in 1992.