When Red is lecturing Donna and Eric before they leave for Jackie's parents' ski cabin, the van they are standing behind is a late 1980s Chevy van.
While reading Jackie's directions to the cabin, Donna says to take I-43. I-43 did not exist until 1981.
Eric drove to Jackie's parents' ski cabin in season 1, so he should already know the way.
Donna doesn't unwrap the "Twonkie" before she inhales it.
Donna and Eric decide to have sex on the kitchen table. When everyone else returns unexpectedly from the cabin, Kitty looks straight ahead into the kitchen and sees them. Moments later, Hyde and Red also look straight ahead to see them, Hyde commenting on Donna's butt. A later scene shows the table to the right of the doorway. Kitty, Hyde and Red were looking at the counter, not the table, which Red and Kitty are then seen sanitizing.