Episode #7.3 - S7-E3
Other mistake: Jeremy is making a copy of Zammo's bus pass - the expiry date on it is 16th December 1983, this series is set in 1984.
Episode #7.2 - S7-E2
Other mistake: When Claire is asking her friends for their dates of birth for her bio rhythm calculator Anita says her date of birth is 25th October 1968, to be in this school year she would have to have been born between September 1967 and August 1968.