The 85% guideline question

Although we have never bothered with it, surely this 85% guideline is now well outdated with modern cars and needs updating. 

The guideline refers to a car's kerbweight, but the term "kerbweight" is no longer applicable and instead MAS (Mass in Service) or MIRO (Mass in Running Order) is used by manufacturers.  Many manufactuers notably Vauxhall no longer publish the car's kerbweight.

Using the above and correct terms changes the 85% guideline for newbies quite significantly and can open up a new market for better spec caravans for a new newbie that their cars are capable of towing safely. 

I have never seen a vehicle devoid of driver or passengers and with no fluids towing a caravan.  Have you?