User blog comment:B214/Volume 22 spoilers/@comment-173.185.123.104-20160909174547/@comment-1359322-20160909175549

What does the baby making room has to do with Irina receiving an Evil Piece? Irina wants to remain as an Angel she won't take in an Evil Piece even from Issei. Besides it's not like she has to accept an Evil Piece to stay by Issei's side in the first place.

And Bina most probably isn't Tiamat, we know Bina is a Devil and she has High-class Devil Demonic Powers, from Tiamat's first appearance she seemed to still be a Dragon not a Devil.