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
Mutt, this is a common misconception. Whilst true for almost all aircraft over, say, about 15 tonnes, there are some manufacturers who don't approach flight test for landing distances in such a, shall we say, focussed, way... When we started flying a small straight-wing jet, we soon found that we were achieving the AFM figures very easily, and discussions with the manufacturer revealed that they hadn't put much effort into minimising landing distances during flight test.
The rest of your answer is spot on, though I would add, from a practical point of view, that the factors applied (1.67 and 1.95) are, in my opinion, somewhat excessive for some types of aircraft. I routinely fly small straight-wing jets and heavier metal, and it seems very clear to me that whereas I would never aim for the piano keys in a large aircraft, we do so with ease and repeatable accuracy in the small aircraft, at the same time minimising touchdown scatter. (I won't comment on turboprops where such visual aiming reductions are permitted). It would be very helpful if we were permitted to use this technique to reduce LDRs, especially given that in Europe, many runways at small regional airports (exactly where we, and our passengers, want to go in a biz-jet) are of lengths about equal to our factored LDR.
Instinctively, a factor of about 1.4 seems very reasonable for these aircraft on dry runways.
Is there any evidence that runway overruns are more common in private operations than transport? I don't think so...