In Florida, one of the statutes defines a "commercial vehicle" as "any vehicle with three or more axles". There is no provision for use, or consideration of vintage.
Three different Florida statutes define commercial vehicles in different ways. So one problem may be:
1) What any state statute defines commercial vehicle as
2) What your local jurisdiction defines commercial vehicle as
Some might use number of axles, some might use weight (tagged or gross), some might look to use (such as "in commerce/commercial"), some might have specifics concerning graphics or lettering (considered advertising), etc. There is no "one rule".
I live in an "unincorporated" part of the County, which simply means it is just the county - no other township or city. Some local jurisdictions are very strict about the types of vehicles.
They have zoning requirements regarding parking of vehicles, including RV's and boats.
They also have requirements about having a vehicle currently tagged.
In Florida, a former military vehicle does not have to DISPLAY the tag, but it needs to have one in the cab to produce upon request. To have a tag in Florida, insurance is mandatory.
My vehicles are all tagged (and titled) "private" and are so insured. They have no signs (except, of course, any military markings). I do not have any vehicle with more than two axles. Thus far, in nine years, I have had no problems w/code enforcement or with my neighbors (who are often the cause of a code enforcement visit....).
So, in Florida, a 712 Pinzgauer (3 axle) is considered "commercial", when a 710 (2 axle) is not. My (new) bobbed Deuce only has two axles - not commercial, but a regular Deuce (3 axles) - commercial.
These regulations were put in place by boards or commissions on the more county or local level, following public hearings. They have the power to enact such restrictive regulations. Their "purpose" is to protect the integrity of neighborhoods - I mean, if someone wanted to collect garbage trucks, would you want them parked next door in your development ? So it is not the intent, but probably more the application of the regulations that is an issue. My point is, what is enacted, can be thrown out - but it is a process. Just because enforcement has been lax, or inconsistent doesn't mean they can't enforce it against you.
There again, also sometimes it might be condition. Some of our "toys" are a bit more on the rough side that others. Some of my toys are too big to keep at my house, and I have to make other arrangements.
I agree that a bit of research invested in the front end might save a bit of anxiety on the back end. Sometimes it is hard to obtain a straight answer. I personally think there is too much management in our lives these days - and the focus is on the petty not the important.
Best of luck in your situation - maybe there is a way to prevail against the "man"....