Shiner,
MANY mdt/hdt's do not even have a factory door sticker in them. Mine doesn't! Its in the owner manual in my office......Being as most of these are sold as incomplete rigs, the door sticker means squat! Especially if one adds a drop, tag axel, wider tires, for more weight carrying capacity! Its then up to the end body builder to install a "CORRECT" door sticker. Even at that, it is legal to add these things later in like, up or lower the GVWR, etc.
From an RV standpoint, ANY if not most of the type a or c motor homes that have tag axels, I would suspect NONE of those axels were installed by the frame, motor chassis builder, or in the case of a C, the van body/chassis builder. ALL after market, a new gvw tag installed by the RV manufacture.
Marty