:: If they test the fuel in the tank and it’s over 10. ::
Ummm, yeah. That covers about 97% of all cars on the road, world wide.
Ethanol is added by batch process at the refinery.
Did you parse that? The cars tank. If you take it to the shop and the fuel tank contents test 11% and they are asses you’re paying for the repair.
By no means is the average refinery batching solid 10% batches for shipping all the time. I’ve heard of pump values as high as 27% for 10% pumps.