Some states had vastly different license plate fees based on GVW ratings. When my grandfather's 34 Chevy flatbed trucks and later tractor/semitrailer rigs were hauling beer from Milwaukee and St. Louis to Nashville, negotiating the GVW limits for several states was a nightmare. A legal load in one state would draw an overload fine in the adjoining one sometimes.

It's possible Chevy learned to sell the same trucks with different GVW ratings in different states to take advantage of loopholes in registration fees, hence the ID plate changes. They knew most owners planned to overload 'em anyway!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!