My two bit...
ALD: Actual landing distance is demonstrated under test conditions.
Having said that, under normal conditions the variations to the test conditions in:-
1.wind 2.QNH 3.ISA dev 4.R/W slope 5. Friction coefficient of the r/w 6.a/c weight & trim 7. height over threshold 8.flare height & technique 9.speed over threshold 10.any more that I missed...
Makes us want to have some safety margin!
The people who decide these, decided that a safety margin of 40% is required for dispatch.(faa, jar, and the others).
So if an a/c under test condition took a shade less than 6000'(5987') to stop for a given wt. multiply 1.67 times gives 10000'
(1825m/3048m respectively in the metric system)
INFLIGHT conditions are generally left to the informed decision of the crew Faa insists on a minimum safety margin of 15% above what one would extract from the QRH
jar is non committal
They do not specify commercial reason or otherwise
As a pilot I would apply a margin as practical and safe as possible on a case by case basis