Forum member "R.T." replied with this on page 4 of the thread:
Here's the scoop: It is to comply with the Federal Motor Vehicle Safety Standards (FMVSS) Act , Standard number 110, which basically states (among other things):
"The Addendum Label is a yellow label located on the driver’s side center pillar. The label provides the weight of accessories added to your vehicle which were not already taken into account in the vehicle occupant and cargo carrying capacity located on the Tire and Loading Information Label."
It is for accessories added at the manufacturers "Vehicle Processing Center" or what some here have referred to as the "Port". Our Frontiers being built in the USA don't actually go through a Port after assembly. So it covers many things most people think of as factory options, i.e., towing package, spray in bed liners, etc. Items added prior to delivery to the dealer and (should be) listed on the window sticker but not reflected in the load capacity sticker in the door. Therefore, the load capacity must have the yellow addendum sticker. The sticker is applied at the Vehicle Processing Center, not the dealership.
"Dealer added options" or "after market" options added at the "dealer", are not required to be listed in the addendum sticker. In other words, if you have a "Factory Spray In Bedliner" it will be reflected on your window sticker and a yellow addendum sticker added to your door frame. If you ask your Dealer to have an after market Spray In Bedliner added before as part of the sale, it will not (or is not required to) be reflected in a yellow load capacity reduction sticker on your door.
The FMVSS applies only to the manufacturer, not the dealer. Therefore, it only applies to items considered "Factory", although they are added at the "Vehicle Processing Center". After market items are not bound by the FMVSS standard (s) in regard to capacity reduction addendum sticker.