I'm not surprised, things were way different back then and I'm pretty sure max towing speed was 80ks as well. Dad had a company car that was constantly for sale. Sometimes he had one car for 6 months sometimes he would have 3 or 4 new cars in a week. It was so frustrating when they sold his car, dad would end up cruising the used car lot looking for anything with a tow bar, we had all the adaptors for the 6 and 7 round and rectangular connectors.
Many manufacturers cut a pretty fine line with the load rating. I know of a few guys that realised their boat was almost impossible to get under 2 tonnes. Resulting in expensive upgrades to relatively new rigs.