can 1 octane make this much difference?

Octane is a true rating, but the effects of storage and mixing can change it. If you are moving thru a certain area of the country, the fuel blend will change. Fuel in New York city is different blends from what I have in CT. We have the 10% ethanol fuel here, and that changes things too. You will be lean if your car was tuned on non ethanol mixed fuel, and then you run it. Add to that the possibility of the tanker filling the wrong octane tanks and mixing up octanes, and the extra water the ethanol fuels attract and hold..and it's no wonder you get some ping with unknown fuel.