I'm a little confused by your question AlphaFrog. Are you asking how many PNM's don't get bids or how many don't accept them or what exactly?
I will offer this as coincidentally I was just printing off a copy of our past years Recruitment Stats from the
UA Panhellenic website. In 2006 78% of all women who attended Open House received bids. 88% were matched to their 1st choice, 10% to their 2nd and 2% to their 3rd. Very few women were completely released.
Obviously we don't know why those who voluntarily withdrew did so. As with any campus, some probably didn't receive invites back to the Chapter(s) they wanted and some decided they didn't really want to be Greek at all.