I can see how this is a little confusing.
The Dean of Students Fraternity and Sorority life website seems to show
here that Panhellenic sororities only have organized recruitment in the fall.
However, UT posts their Spring 2014 Pahnellenic grade rankings
here and it clearly shows that almost half the sororities have new members.
I found an old post from the Texas Panhellenic website
here that possibly explains how Spring Recruitment works.