I shan't go into laboured discourse .. however, I wouldn't like to go to Court and defend whatever on the basis of your argument ...
Courts are about laws. There is only one law in this case:
Thou shalt not take off overloaded.
But if you took off with the temperature at 41, when your charts only went to 40 degrees, how are they going to prove that you took off overloaded? They can't use the charts because they are not valid.