Good luck.
Roughly 3 years ago, I took my '58 Tx Farm Truck plates to my local tax office and successfully registered my truck. When I talked to the same office a couple of months ago, they told me they would NEVER allow someone to register an antique with Farm Truck plates because it isn't for ag use...
My point is: not only do different tax offices interpret the law differently, it is possible for the SAME office to offer different interpretations depending on when/who you talk to them.
My recommendation is if you find an office giving an interpretation satisfactory to you, pounce on it. If they don't give you a satisfactory interpretation, keep trying at different times and locations.
We tend to think "the law is the law", but I assure you, it isn't. (That's why there are lawyers.

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Bill