The certification requirements specify a landing demonstration from Vref - 5 at the threshold, without power intervention; thus touchdown speed could be lower.
Performance data calculated by the OLD/FOLD method is based on the planned speed at the threshold, and a speed loss of 7kts during the flare.
The baseline is Vref, thus any approach speed additive - any planned for adjustment at the threshold, must be considered, which will increasing the landing distance required.
As yet no guidance has been found for adjusting distance for speed additives retained during the flare.
A sensible interpretation would be to use the planned threshold speed plus a further 7 kts as the basis for landing, which could result in a very large distance increment:
AC 91-79B 5.2.2 Excess Airspeed; (at the threshold),"
As a rule of thumb, on dry or wet runways, a 10 percent increase in final approach speed results in a 20 percent increase in landing distance. "
If the additional speed durning the flare was considered in a similar manner as a tailwind, then "
The effect of a tailwind increases the landing distance by 21 percent for the first 10 kts of tailwind."
https://www.faa.gov/documentLibrary/...91-79B_FAA.pdf