Eric's High School Reunion states he graduated in the "Class of 1979". In Season 5, Episode 25 ("Celebration Day"), their tassels show "78" (for Class of 1978). Jackie graduates a year later, which has to be 1979 because the final show is New Year's Day, January 1, 1980.
During Eric's dream sequence, Jackie is left out in the snow. It falls heavily behind her, as she sadly peers through the window. None of the snow lands on her.