Is it law though? I don't know about you guys, but I'm about done with bending over and if the retailer isn't required to have the number, I'm inclined to let the ammo collect dust on their shelves until they smarten the F up.
I suppose if it is not req by law, some of it may be company policy, KYA stuff or perhaps something that comes from something "they always did" but in reality if you want ammo and want to go shoot, not giving my info is not the hill I will die or even fight a battle on.