Revealing mistake: In the warehouse, after Michael calls him, when KITT busts through the door, the plastic sheeting used inside the driver's window to hide the stunt driver is noticeable.
Other mistake: When Michael and Marty are being chased and shot at, K.I.T.T jumps over the top of a hill. In the next shot of K.I.T.T driving away, you see a wheel trim rolling down the hill which has fallen off K.I.T.T. (00:39:45)
Answer: I would say that unless there's visual evidence it was another K.I.T.T. car, as in you could see the bar scanner or cut steering wheel, people on here would correct the mistake by saying more than one 1982 Pontiac Firebird Trans-Am was sold and there's no reason it's meant to be a random car.
Bishop73