FE's and LM's
I do believe you have just made a case for carrying Flt Engs and Loadmasters as an integral part of any cargo crew!! I also find it hard to imagine any crew worth its salt not detecting a discrepancy between planned fuel load and actual fuel in tanks, presupposing the guages on the flight deck are "reasonably" accurate, a few gallons maybe!! It is an added advantage if the crews operate the same airframes again and again, in the small company I worked for the crews new individual frames so well that their fuel calculations were on many occasions more accurate than the CFPs!