Jonski: Last time I tried to fill in one of these, it asked not only for the rego, it also required the make, model and colour of the vehicle. Which A) is a lot to remember until you can pull over and jot down the details and B) requires being able to identify unfamiliar models or those with no insignia. Not to mention trucks or buses which are custom jobs.
YMMV.
I used carjam.co.nz to jog my memory a bit about the exact details. Also noticed his wof/licence was out of date. So hopefully they do something about it.