Well in the past, our aircraft; (extinct Luton based airline), were sometimes heavier than we thought, because we used standard passenger weights. Once in the cruise, I used green dot to work out the actual aircraft weight and it was sometimes 2 tonnes above what we had calculated at the gate.
One season, we subbed for another Luton based airline, and their standard weights were higher - 93 kg for a male, whereas we used 88kg - I cannnot recall the female figures.
And yet there was a hell of a fuss if the wrong catering weights were used - even though that only made an error of a few hundred kilos.