Hmmm... not sure the WO are totally representative, they had more than the 62.5% covered by AS, I guess especially in the lower levels. They might not have been that much luckier with the highest ones, since testing isn't compulsory. They test women who come to them and they deem WO potential. They only take without questions all sparkers.
There's a quote from Egwene or Elayne that apart from finding all Sparkers, the Wise Ones claim to find all women with dormant ability as well. From the Wise Ones I doubt its an idle boast.
Not idle as they believed what they said, but apparently they were quite short of finding all. At least RJ has removed a good percentage of women they would miss for lack of any systematic testing. They get all sparkers. ALL. They train any woman who become an WO apprentice and can learn, not matter age or strength. They do not test any woman who didn't approach them or wasn't approached by them to be a WO apprentice. They just think they have a "nose" for finding learners, but really they don't.