That is correct, the lead did add octane back in the day, but these additives do not have enough to make any difference. When the lead was taken out, they suddenly realized that the lead was lubricating the valve seats on older engines. When it was gone, the engines started eating up seats. Now they are made harder and do not need the lead or any other lubrication. A much smaller amount of lead is necessary to lubricate the seats than is needed to add octane.