There is one thing many of you seem to be forgetting.........
The fuel was never exposed to -70 outside air temperature (SAT or Static Air Temp). The wings and fuel temperatures would have been much warmer due to the heating effect of Ram Air (TAT or Total Air Temp)
The coldest the fuel should have been during the flight is -37C.
Lost in Saigon;
That is not true of the 6 different aircraft types I have operated
(Lockheed, Boeing, Airbus) In my experience any prolonged exposure to a SAT of -60 or more has caused fuel temps well below -37C and required a modification to the flight envelope. The small Airbus models are especially affected.