Messiah, final fuel is found from the fuel receipt provided by the refueller which includes the quantity in litres and the SG. Any overfuel is calculated and then added to the final loadsheet weight provided by load control. Load control have no knowledge of what the final, actual fuel on board the aircraft is - only what the planned fuel is.
SG is therefore allowed for and cannot be used to explain any discrepancy. If we calculate thus, we are overweight and are NOT legal!! To the best of our knowledge, if we are up against a limit like this, we are overweight and must take appropriate corrective action. No ifs, buts or maybes.