First, I am not a lawyer. Yes, there is alot of confusion on what a truck is rated for. Yes, there is the sticker on the truck (10,000) yet I get a truck registration from the state saying (12,000) and I have to pay the bill for that one. I have read that for some time period (not sure when) the makers derated 1 tons to let people driver without a CDL. Thus alot of 1 tons that have the 9,999 GVW rather than what they are really rated for by the makers. Your truck is ALWAYS limited by the weakest link, be that tires, axles, brakes, trailer brakes and controllers, etc.
As to legal, I would agree if it is not your fault doesn't matter. Not sure it matters if it is your fault. Insurance still covers... heck don't they cover if you are drunk and hit someone?
FYI, Light Truck tires are de-rated by 10%, they figure everyone overloads them. Although this site doesn't have the reserve amount they do mention it - Tires branded with the "LT" designation are the "little brothers" of 18-wheel tractor-trailer tires and are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo.
https://www.tirerack.com/tires/tiret....jsp?techid=46