Factual error: The famous AFC Championship game that featured "The Drive" took place on January 11th, 1987, while the events of the film took place in 1986.

Hot Tub Time Machine (2010)
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Directed by: Steve Pink
Starring: John Cusack, Chevy Chase, Crispin Glover, Rob Corddry, Lizzy Caplan, Craig Robinson, Clark Duke
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Trivia: When the foursome ski down the mountain and are looking around at the oddly dressed people, someone behind John Cusack says, "Hey Lane, you owe me two dollars". This was a nudge to John Cusack, who played Lane Meyers in "Better Off Dead" and was pursued in the snow by a crazed paper boy shouting "Two dollars!"
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Answer: It's just the rule they used for the movie; not a lot of thought was put into the time-traveling rules with the obvious inconsistencies the movie has throughout regarding it, especially in the ending.
lionhead