When Jackie drives to her father and stepmother's house, she sits on the right-hand side of the car (as is normal in the UK). But when she drives back, the footage is the exact mirror of the drive there, with her sitting on the left.
When Sheila Keith's character is giving Tarot readings, she deals the cards and lays them out in front of the subject - but the participant in any reading is supposed to choose and touch their own cards in order for it to predict what may happen in the future.
Debbie states her age as 15 to her sister. That makes her birth year as 1959. Her parents were sentenced to a mental institution in 1957, which would make it two years before she was born. The film was shot and set in 1974. (The vehicles registration plates confirm this).