Folks,
As an old and far from bold pilot, with around 50 years in the business, such discussions as this really concern me!!.
All quasi-legalistic and ignores the real world, lulled into a very false sense of security because modern aircraft are so reliable, and serious non-normal situations may never be experienced by a pilot in a career --- outside of the sim.
And, believe me, real world emergencies never run like a sim. exercise --- that is when you find your personal proof of Murphie's Law.
The whole reason for "factoring" was/is because the "average" pilot cannot achieve the un-factored distances in the real world.
Not even close!!
So, if you commit yourself to a landing, and you have only the raw distance available, you are going to go off the end ---- and reverse thrust, which is not accounted for, is not going to save you.
If it is a "do or die" exercise, an uncontrollably fire, or minutes of fuel remaining, or some such dire situation, where running of the end is the least of your worries, so be it.
But for most situation, remember you are not a test pilot flying under test condition. So don't plan to be!!
Personally, I do not care what might be "legally" permitted, what phase of flight it might be, from pre-flight briefing to beer o'clock, except in extremis, as PIC I will want "real world" runway lengths available, 1.67 is good, more is better.
Tootle pip!!
PS: As my Christmas T-shirt says:"Common sense is now so uncommon, it should be re-classified as a superpower"