I'm not interested in arguing either but it is important to have information as accurate as possible for other readers.
The 200 kg isn't "built in". The Nissan stamped GVM is the gross mass the vehicle can legally be.
You can't load a 3000 kg GVM plated Patrol to 3000 kg and then add 200 kg extra in any shape or form, towball or otherwise. You will then be 200 kg overweight on any weighbridge.
The reason the posted reductions don't match actual weight is because of the increasing effect of the weight on the rear axle. Not only is the increased towball mass adding more weight to the rear axle by leverage but it also transfers weight from the front axle (hence why people use Weight Distribution Hitches).
Nissan are saying that you should reduce your allowed GVM by 290 kg before you add the 350 kg towball mass which is still part of your GVM. You effectively lose 290 + 350 kg from your original 3000 kg GVM. This is to prevent the excess on the rear axle exerted by the towball so far back.
Nissan are not saying "Hey, now that you've added that enormous weight to your rear axle, have another free 60 kg to throw in on top of that"
The Navara advice is a bit clearer with their sliding table. They have a very clear "Reduce Loaded Vehicle Mass" column.
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Navara.PNG