The lawyer's answer is that no further factoring is required. The normal ops landing distance factor is purely a planning consideration, once you are airborne you use actual distances for calculations.
However, it's a bit of a no-brainer that if you have a choice of places to land flapless/no anti-skid or whatever, one has 1 metre more than the figure you've calculated and the other has a lot more - which do you choose?
