I think the main point is if you land your jet at a particular speed because that correlates with the weight you *think* you are, as long as you are not grossly wrong in your estimations, the landing run will be pretty much the same, whatever weight you *actually* are. Much in the same way that if you tried to land even a lightweight aircraft at Vref+80 (has been tried), you’re probably going off the end unless it’s a very long runway.
That said, errors have a nasty habit of compounding, so you should use the most accurate available data in calculation but be aware of the tolerance in the result. Accuracy vs. precision and all that.