If you fill to the first shut off every time the overall average will be right...individual fills could be slightly off.
My brother and I both have 2016 platinums. We both fill at the same pump and his display is very close to exact. less than 1/2 of 1 percent error. This is the kind of accuracy I experienced with my 2011. My 2016 seems to be between 3 and 4 % off. It always takes less fuel to refill the tank than what the display indicates I've burned.
After accounting for the less fuel that Ive used my mileage is still not satisfactory. Last trip was 8.7 miles per US gallon ... round trip, 75 mph, 100" inch wide trailer, GCVW was 23400 lbs. The truck handles it like there is nothing back there on most hills but saying Ford together with fuel economy is an oxymoron as far as I'm concerned. My brother gets very similar mileage pulling his trailer which is the same width and height but about 2500 lbs lighter. I also have three brother in laws, each with 2015 F350 SRW Platinums and although it is very difficult to get any one of them to say a negative word about a Ford truck they all get similar milage to mine.