I've only heard of one place where the manufacture's recommendations have legal status (for smaller RVs and tow vehicles). British Columbia I understand legislates GVWR per the owner's manual.
Tow rating, for smaller vehicles tend to be marketing department dictated, often grossly underestimated to up-sell people to large trucks for cars and SUVs and given they don't know how the trailer is setup for a vehicle sold with not even a hitch let alone a known setup they can never be all that relevant.
A larger pickup truck yes then the engineering department starts to have some say on the true capability, and the penalty for overloading rapidly becomes a bigger issue.
