Actual landing distance is established during certification with a firm landing and exuberant efforts at stopping, hence the requirement to factor this distance for mere mortals PRIOR to takeoff.
However, once in flight this factoring is no longer required, you can land on a runway that is the same length as the ACTUAL landing distance. If you have a QRH requirement to factor this distance, you can legally land on that factored runway length.
But the big question is do you want to? Are you a test pilot? If not, then i would suggest that you take your factored landing distance and apply an additional percentage. This percentage can be 10%, 20% or up to the full pre-departure 40%, it all depends on the aircraft condition and and how you feel on the day.
Mutt