J2807 will help...just a bit, as there are many, many wiggle spots for
the OEM marketing folks to play...my guess after decades in dealing with
specifications and regulatory agencies...and my internal marketing folks
Not automotive, but industrial controls for military/black-badge/gov/commercial/people-movers/etc
All spelled out in the fine print, and not just in one spot, but everywhere
where there are ratings.
Most just want a label to tell them everything. Most do NOT take the
time and effort to go out and actually weigh their whole setup.
The labels are getting better, but I still adhere to weighing it...especially
if you have after market stuff...plus whatever you load in/on the TV
My GMC 1996 Suburan K3500 SLT is listed by the OEM to Calif DMV as
5,250 lbs curb and at the local garden scales just under 7,200 lbs with
me (180), toolbox (+200lbs) and misc stuff.
But folks still believe theirs weighs in at curb. The current door
label listing cargo or payload is pretty accurate. A fellow member
used to work for one of the OEMs and owned that label process. Said
it is computer generated via each option listed. Must be accurate as
it is part of the shipping info (billing by weight)
{edit} pic of my sub

mysub mysuburban K3500Sub