The Goodnight Kiwi that was shown on the TV during Shutdown was the incorrect version for the period. The film used the early 1990's version with the TV2 logo at the bottom at the end. In 1984, it should have ended with the message "Goodnight from Television New Zealand".
The plastic road markers that "Boy" was playing with and bending down on the side of the road were not found anywhere in New Zealand until around 1990. The film is set 6 years earlier when wooden road markers were in use.
The cattle down have National Animal Identification and Tracing (NAIT) ear tags which did not come into effect until the 2000s in New Zealand. RFID reader tags did not exist in the movie's time-frame.
In the opening scene there is a decrepit old truck with a bent old license plate "ME1831". License plates in New Zealand were released alphabetically starting with AA and culminating with ZZ before the system switched to the a three letter, three number system. "M" license plates were first seen in about 1985 - a year after this film was set. A truck that old in 1985 would have had an A,B,C or D license plate.
While driving, Boy and his dad pass a yellow warning sign. These signs were not used in New Zealand at the time of the film.
The story takes place in 1984 with a month ending in 'mber' ( i.e. September, November or December) according to what is written on the classroom blackboard. Boy says that his brother Rocky is six years old. Their mother Joanie died while giving birth to Rocky. According to Joanie's tombstone, she died in April, 1977. Doing the math, that would make Rocky seven, not six.