We know how it was arrived at and when. The point is, how relevant, accurate a guide it is.
My a/c has a "demonstrated" 12knots the day it was certified 55 yrs ago, I, with just 250 hrs have little problem with 20knots, I am sure that in the hands of someone who can fly, an even higher figure could be achieved. So what is the point of the 12knots figure?