Not all fuel stations are honest. I know the state of Michigan has a team going around the state checking fuel pumps, to make sure you are getting the fuel you are paying for. Some have been caught with their pumps not putting out a full gal. when the pump reads for a full gal.. That could be why some say they have put more in their tanks, than the tanks can hold. Also, how much does the filler neck, fuel lines, filter and things hold.
I haven't ran mine out and don't intend to, to find out how much it holds. I'll go by what Ford tells me.