The final game of the season at Anfield kicked off at 8:05pm, it was nearly 10pm and dark by the time the match had finished (as you can see from the actual footage of the game) yet when the celebrations are going on back at Highbury it's still light.
A woman at a party is given a present and leaves without it, gets in a taxi but she's got no handbag or purse and no pockets in her dress.
Presumably because of a placement deal, many of the characters are shown drinking Holsten Pils, including the protagonist during the crucial match and Arsenal fans celebrating at the end. In the 1980s, Holsten were sponsors of Tottenham Hotspur, Arsenal's great rivals, and there is no way Arsenal fans would be drinking their lager.
At the party, Sarah turns on the TV to find out the score in the match and immediately announces it's "still nil-nil". But in 1989, TV broadcasts did not display a score graphic in the corner of the screen, so she would have had to wait until the score flashed up, which happened every 5 to 10 minutes, or the commentator mentioned it.
When, as a child, Paul Ashworth goes to see the Reading FC game, the Reading FC Club Badge on the rosette of the supporters is the one which did not come into being until around the 1987-1988 season. The badge that should have been worn in the 1970s, when the match took place, was the old style 'Elm Trees' badge.
At the leaving party that Ruth Gemmell attends, a Lisa Stansfield song plays in the room. That would not have happened as the track was released six months later.
Once on the terraces and later in the celebration scene, there is a man wearing a Boston Celtics cap from a much later era.
In the first few minutes of the movie, Ernest Hemingway's name is misspelled as "Hemmingway." As Paul is an American literature teacher, this is a curious error.