Dry weight Heavier than labeled?

So as we have been traveling from Washington State to South Dakota in our new to us 2023 Beacon 42RKB I was using the label listed dry weight on our unit. We sold our house, almost everything we owned and then when we bought this coach, I would not let anything go into the coach unless we weighed it and kept track of what was the total weight of our things.

Now I knew we would miss a couple things and probably be up to 100 pounds off on the tracked weight, but I was SHOCKED when I started our trip with a stop at the local CAT Scale.

I found that the GVWR was off by about 1500 lbs!!!

I was dumbfounded how I could have been so far off. Then I remembered that when we bought the unit in Sisters Oregon, I had weighed it at the Madras CAT Scale.

We had stayed in the coach for a day, and I knew it had some liquid in it from when the inspection had been done on it since it was a “used” unit. So I know a few pounds form waste was onboard at 8 lbs a gallon. But certainly not 1500 lbs worth. (1500/8= 187 gallons).

When we had dumped it, the waste was no where near more than 15 to 20 gallons.

So I say all that to pose this question, Why is my unit @1500 lbs heavier than listed on the dry sticker of my coach?