[mike16]

State DOT regulations also influence which year the vehicle "is"

In some states the year the vehicle was first resgistered is the date of that vehicle.

It caused alot of problems and a few surprises. sometimes it was used to manipulate the value of a vehicle. It caused problems if a vehicles was sold out of state or imported from a foreign country.

I think, that by the early 80's most state DOT regs fell into line. Commercial vehicles esspecially larger trucks remain a bit of a grey area if they went to another manufacturer for specialty body work before going to a dealership or directly to the end user/customer.

State and federal vehicle emission regulations also compelled states to become more uniform in designating or assigning a year of manufacture.