Anachronisms: The family is watching Thunderbolt and Lightfoot (1974) on TV, which was not even released to theatres until 1974, but we later see a date on a gravestone of 1973 (which means the TV scene was probably set in 1972, since there was an intervening New Year's Eve scene).
Continuity: Billy is shaving with shaving cream on his face while talking with Channe, but in the very next shot the shaving cream is gone.