Certain fragmentary manuscripts, largely forgotten, contain tantalizing hints about the nature and use of circles in the Age of Legends, but unfortunately only hints. According to what the circle was intended to achieve, members were recruited depending on their strengths in the Five Powers while the leader was chosen more for skill. It also seems that certain balances of male with female were considered best for certain tasks, and also certain sizes of circles. A circle of seventy-two may have been the largest and most powerful combination, but it was not always the best for the desired results. Some tasks were best accomplished by a circle of one man and one woman, despite its limited strength, while others were more efficiently done with greater numbers. The details remain lost in the ruins of the Age of Legends, although it is possible that there may be sources hidden away in the library of the White Tower.

Its pretty clear that

a) Smaller circles could sometimes do better than a circle of 72.

b) Individual member's strengths in the power as well as the skill of the leaders mattered a lot.


Given the nature of the Seals, I'd bet they wanted thirteen AS strongest in Spirit, and also extraordinarily skilled. That must be a sufficiently rare combination as to exclude the strongest women.

Weaker women like Sorilea have shown skill, yes, but nowhere close to what even women like Egwene show, and I believe that was the minimum level of strength they considered for inclusion in the circle.