Regarding weight
As most carriers use averages for baggage weight & passenger weight but actuals for the AirCargo units, the most likely area for weight error is not the air cargo (Frt, mail) load but rather in the bgge / pax weights. I know there is a fudge factor built into the W&B but have always wondered how close the average wt was to the actual all up load (Pax, Bgge & Cgo).