The number plate "GC85" was originally issued to a 1972 Holdan Torana on the 7th June 1972. The plate does not belong to the 1980's holden commodore.
When the two main characters are starting their journey out of Auckland the camera shots of them in the car driving show the passing scenery is on a diagonal point of view clearing indicating the vehicle was in a towing configuration and not actually being driven.
Although the movie is based around the 80's when the girls in the Holden commodore meet up with the boys in the blue holden that catches on fire, the blue holden had a WOF from 2002.
When the two main characters arrive at the "Private Property - Road Closed" bridge (where they first meet the two girls), artificial lighting is illuminating the scene. There is no possible way a street light or moon light could create such strong lighting effects, especially in the countryside.
When Grant and Paul leave their house at the beginning, the scenes of them driving are completely out of order. The first shot shows them very close to the Auckland CBD, followed by them driving down State Highway 1 in the country (nearby Rangiriri), then passing under the Papakura Motorway bridge (part of Auckland), back again on the SH1 country road and past the Japanese bus they encounter, until the car turns off at Pokeno (which is much further north of Rangiriri and just south of Auckland) to head west.
When the boys turn off the expressway and come to the sign "West Coast (37)", this is completely in the wrong location. Highway 37 is several hundred kilometers to the south in the Waitomo region. The sign "West Coast (37)" was a prop used at Pokeno, just south of Auckland.