Mine's been assed at $500 in two different towns in CT and I do not have a vintage or antique plate.
Only requirement for an antique plate is 25+ years old.
From the CT DMV.
According to state law, any antique, rare or special interest motor vehicle, as defined in section 14-1, shall be assessed at a value of not more than 500 dollars.
DMV: Classic Vehicle Plate
Sec. 14-1. Definitions. (a) Terms used in this chapter shall be construed as follows,
unless another construction is clearly apparent from the language or context in which the
term is used or unless the construction is inconsistent with the manifest intention of the
General Assembly:
(2) “Antique, rare or special interest motor vehicle” means a motor vehicle twenty five
years old or older which is being preserved because of historic interest and which is
not altered or modified from the original manufacturer’s specifications;
http://www.ct.gov/dot/LIB/dot/documents/dbikes/14-1.pdf
The different use of commas is interesting.
The first links description uses commas that I'd interpret as "OR" statements, but the actual description it defers to combines all the requirements.
You should probably also find out how your assesor is determining if a vehicle meets the historical interest requirement.
What value did they assign to your car?