1)
Why does it say "Ziknei ha'Edah"?
1.
Malbim: The Sanhedrin investigated whether it is possible to permit the Shevu'ah, for when they swore, they did not intend to kill the women of Binyamin. They never intended that men of Binyamin die childless! This is a Pesach 1 of regret (a reason to consider the Shevu'ah mistaken).
1
This seems like the opinion that allows permitting vows via Nolad (later developments that one could not have anticipated). We rule like Chachamim, who forbid (Nedarim 9:2)! (PF).
