I was there when it happened and the truth of the matter is that Shell
oil wanted to stop stocking 80 octane avgas. Without any testing they simply took 100 octane Avgas and RAISED the lead content to 6 Grams per Gallon and called it "Low Lead"
By doing this it could be run in the older aviation engines. The FAA bought the idea and 100 octane Low Lead was borne.
That is twice the lead per gallon than pump gas ever had. You can count on having to deal with all of that lead if you run the stuff in any car.