The older standards envisaged a maximum 20kt approach speed exceedance
I vaguely recall reading an incident report about a German registered 737-200 that over-ran the runway. Seems he had the full 20 knots additive to his Vref for Flaps 40 and touched down with all the additives. Now this is where I get a bit vague but I am sure the investigation came up with the fact that at Vref 40 plus 20 knots touchdown speed, the lift was equal to the weight and the 737 would not "sit" down.
I know that spoilers must come into the story somewhere but maybe they did not actuate because of no weight on the wheels for that few critical seconds of skimming along the runway?
Maybe that is why the max additives are 20 knots?