User blog comment:B214/Volume 22 spoilers/@comment-189.14.202.69-20161016140306/@comment-29963364-20161018051904

If the latest generation of a Devil Clan's members have "Mixed-Heritage" (meaning they share blood with different races), and the Clan cannot, or is not likely to produce "Pure-Blooded" offspring, then they lose their status as one of the 72 Pillars, becoming "Extinct."

If a Clan becomes "Extinct", any child born from that clan afterwards won't be considered a High-Class Devil (unless they go through the promotion process). They can still be born with, or aquire power that matches or surpasses a High/Ultimate-Class Devil even if they aren't High/Ultimate-Class themselves.

However, it is likely possible for an "Extinct" Clan to restore their status by producing a "Pure-Blooded" offspring and showcasing their power.

Aaaand I guess this could be another possibility for Bina Lessthan's identity and reason for hiding it.


 * She wants to hide her identity so that she'll be evaluated on her performance without her clan's status influencing it.


 * And she's testing Issei to see if she can advance her agenda by being his Official Queen.