172, ‘valid landing performance’, no such thing before the landing, only judgement of the unknowns: wet or flooded, what about all the conditions in between. Who measures / reports the conditions; the same with wind, at least +/- 2, so allow +/- 5.
There are few absolutes in flying other than the position where you stop; assumption kill, so concentrate on minimising all other variables, speed, touchdown, bakes, etc … .