When Rockford is driving round LA looking for the theatre where Inga is working, the shots show his Firebird as both 1974 and 1975 models. Later, when the brakes are cut, the car is a 1977 car. They can be told apart by the front grilles which are distinctly different shapes.
Lauren is left alone in the middle of a street as a car speeds towards her, but her hair has much more curl minutes later when she and Jim report this to the police.
During the attempt to kill Lauren Ingeborg after dinner with Everet Benson, the rear wheel of a blue, 1st generation Ford Mustang is shown burning rubber as the car starts to accelerate. When Rockford maneuvers his Firebird between Ms. Ingeborg and the speeding car, the approaching car is a light yellow 1976 or 1977 Ford LTD sedan.
Rockford starts off in a 1977 Firebird (quad rectangular headlights) and then is shown driving a 1974 (round headlights with blinkers below the front bumper) and then it changes one more time into a 1975 (blinkers in the grille next to the round headlights).
When Arthur is talking with the others in the hotel room, he says that everybody but Noah stays in Los Angeles. Immediately thereafter, the scene cuts to the middle of him saying something.