Is it possible that some pnms didn’t get a bid ?

It's pretty rare but it happens. It's usually either because

a) you're known by at least one chapter to be a horrible person (and houses talk btw) or you have inappropriate stuff on your social media

Or

b) You are invited back by the max # of houses for a round, but you are ranked lower on their lists and you ranked the less competitive houses at the bottom of your list. Then, you get dropped before pref round by the houses you had left, and you are no longer on the lists of houses that would have given you a bid because you dropped them. A lot of these girls get snap bids though.

Or

c) you're a junior with low grades. If this is you, you really have to make sure the houses like you in other areas. COB is probably better for this group tbh, but some still get bids in formal recruitment