When Amy and Paul are playing in the arcade, he suggests that they play "Space Invaders" which didn't com out until 1978, two years after this episode takes place.
Amy goes back in time to 1976. At one point, she says "It makes me feel like one of the girls from Three's Company" which the character "Paul" seems to understand. Three's Company didn't air until 1977, one year after this episode takes place.