Rachman,
That is not correct.
On several types, including for example B744, seating of passengers has no effect on mass & balance calculations.
B737 is also not that critical by the way.
The aircraft seemed to be accelerating to flaps-up speed when the upset occured. This might have nothing to do with a botched g/a, but with flight controls and icing.
What will be the effect of a wing when the Leading edge devices retract on schedule but the leading edge itself is seriously contaminated?...