The First Blood marquee in the opening shot says the film has a "15" rating. That certificate was introduced in 1984-85, part of the Video Recordings Act. In reality, the film was rated "AA," meaning "Passed as suitable only for exhibition to persons of fourteen years and over. When a programme includes an 'AA' film, no persons under fourteen years can be admitted."
The ambulance that brings Lee Carter to the movie theatre has a Road Tax disc, valid for 1 year, that expires in February 2008, and an E registration number plate (license plate) from 1987-88. Many modern cars are in the background, including a 1990's Renault Laguna and a 2001 Vauxhall Combo van.
When Will is gets the stew pot out of the oven, he places it on the table using a cloth with two pockets. In the next shot, from behind, he takes the lid off with his bare hand. In the next shot, from the front, he holds the lid with a cloth.
When Didier Revol demonstrates his acting to Will Proudfoot in the church, a cigarette is in Didier's left hand. When he "shoots" himself in the head and falls to the ground, the cigarette vanishes. The smoke is in the foreground in one shot, but Didier never put it down.
When Will watches the pirated version of First Blood, the cinema curtains open on the film's opening credits. In 1983, all films screened in British cinemas started with the British Board of Film Classification's certificate just before the start of the film. If Lee started recording after the certificate was displayed, the curtains would've been open when the opening credits began.
The brick wall at school shakes when Didier's entourage shakes Lee against it. (According to director Garth Jennings at 58:10 in the DVD commentary, it was a fake wall built by the production when the screenplay called for action in a narrow corridor.)