Downweighing a van from 3850kg to 3500kg

I guy's. Long Short. I feel in love with a camper and drove almost 5 hour's to buy it and drive home. All went well with chasis plate saying 3500kg. Then all of a sudden as i was trying to insure it to drive home the insurance company ( Dolmen said they can't insure us because the van is coming up as 3850kg on system). We quickly checked the log book and yes 3850kg along with a sticker inside hidden well in the cab. So left it there and came home heartbroken..
That following week the man who was selling it felt so guilty and such nice people he arranged to get it downgraded to 3500kg and paid for all new plates etc. Him and his wife even drove the 5 hours down to deliver it and got the bus back ( I think my broken heart was very visible and a few tears hahaha).
So he brought the van to be weigted in and its 3000kg . He sorted all for plates to come directly here with the tax book. I will bring it for DOE ( empty) and please god they will re enter new details as 3500kg limit and we will be away....
So the only thing I'm curious about is getting stopped for overweight. Obviously 3 kids and 2 adult's and all the rest will very likely push over 3500kg if we were stopped and weighed.
However ive attached a comment I read which I found very interesting. So basically they were driving legally on a b license. The weight was only over in comparison to the plate and not what the van was designed to safely carry. The van brakes and suspension etc were designed and manufactured to carry 3850kg so unless they could prove that the person was driving the vehicle unsafely they were not prosecuted??? It was only overweight by chasis plate for b license permission but not unsafe as still under the 3850kg manufacturer safety weight and can handle that 3850 safely because it was built to. So unsafe driving had to be proved which couldn't and no prosecution.
It was a very interesting read and I wonder if any of you wise people or lawyers might know if this could br true or myth??? It does sound good to me and if a real thing I would feel less paranoid driving around incase I was overweight.

I'd love to know your thoughts on this any anyone who might know the legal stance on it. Hopefully it might help other's in similar situation also if it turns out to be a fact

Thank you
Jenny

A very interesting scenario, which I've often thought about.
Forget about the licence bit but consider the 'overloading'.
So the plate says, for example, 3,500kg and the actual weight is checked to be 3,800kg.
However the sum of the axle weights is 3,950kg and both axles are checked as operating within the plated axle weights, which means the vehicle can technically be uprated to 3.950kg.
Given the above, the vehicle would not be being operated in excess of it's technical maximum carrying capacity, its M.T.P.L.W.
It probably needs a prosecution for 'overloading' to determine if the above defense would be successful.

Havnt used Sprucefield. Think the last one I used was up at Toomebridge. There's one on the A1 at Loughbrickland. I'm not that worried now since I got it uprated but if I'm passing a weighbridge I might nip on