When Det. Tyler looks at his shield and ID for the first time in 1973, the shield itself is number 0273, but on the ID card, under "SHIELD #", it says 8847.
In the first two episodes, shots of the World Trade Center show the television antenna. The antenna was not added to the north tower until 1978.
In the premier episode, Sam Tyler arrives in 1973 and a reference is made to someone going home to watch Laugh-In (1977). The character says he loves Goldie Hawn on the show. Goldie Hawn last appeared on "Laugh-In" in 1970. "Laugh-In" itself aired its last episode ever in March 1973.
When Sam Tyler awakes and notices the Twin Towers, the towers look totally complete. In 1973, even though the towers were dedicated, they were still under construction. The film looks as though it was set in the summer. At this point, the tops still had cranes and no cladding on, while Tower 2 was still in the process of being clad, although almost complete. For reference, pictures of the towers in May that year showed a good 20 levels of Tower 2 still showing bare frame.