I think what you will find is that there is a lot of misinformation or lack of understanding the statutes out there when trying to figure out the correct meaning of weight when tagging your truck and RV. At least that is what we just went through in Kansas. Our truck empty weight per the title is 7420. Our new trailer GVWR is 14220 although our actual loaded weight when we hit the road is just under 12000 (verified by scales). When we went to correct how our truck was taxed (the original title said it was a car), they said we needed a 16-20M tag which covers the GCWR and they wanted $291 just for the tag with property tax on top of that.
I knew that wasn't the way our previous truck and fifth wheel was tagged and the weights were nearly identical. So I checked the statute and it states the trucks tag must cover the truck and the towed trailer except RV's for personal use only are limited to 12,000 pounds total. Well it seems most motor vehicle and appraiser's offices miss that little sub section of the statute. I even called the state dept. of motor vehicles and the gal I talked to was not aware of that sub section. Long story short, I took a copy of the statute with me when we renewed the tags and MV agreed and reduced the tag to 12,000. The appraiser's office still insisted it needed to be 16-20M.
We now keep a copy of that statute in the truck so in the likelihood (probably pretty rare) that we are ever stopped for a weight check, we have the proof of why it is tagged the way it is.
We are also on pretty firm ground because that truck never tows anything except the trailer. That might be where the original poster came under the other tagging provisions because he said he pulled other trailers. In KS, if you pull other trailers, agricultural or commercial, you fall under the heavier weight requirements.