[Werner]

I have a general note about engine oils.

I do not know how strictly that is regulated in the USA. But in Germany environmental protection has a very high say in the oil mixtures. For example, phosphorus and sulfur must very barely added.

However, phosphorus and sulfur are excellent emergency lubricants in the limit lubrication range. (Top dead center cylinder/piston, Outlet-valve stem.)
Overall, therefore, discussions are fruitless over then and now, because it did in the past not know better then today. And no lubricant manufacturers is interested today, because the sales volume of vintage oil is uninteresting.