Nevertheless, I do think those who aren't found, or abstain, or do not become Wise Ones for any other reason, would be randomly spread through the bell curve. The Wise Ones don't reject the very weak, and I doubt they pressure the very strong into joining.
They refuse no one, and they train all sparkers even if for some 'unsuitable' ones it could mean a life as an apprentice. Strength don't matter. They just don't really find all learners, not quite. They find all those among the women who ask to be WO apprentices, so it's just that many more do than come to the Tower these days and for the centuries since its big loss of prestige.
So yeah, those they miss would be randomly distributed.