Last intel that I have is that they were hoping to be able to have the next new hire classes before the end of May, but now it looks like it will be sometime next month. As such, there probably isn't as much of a rush, and my guess is that they are evaluating applicants from several rounds of interviews and building a "pool" to draw from as opposed to hiring from each round for successive classes.

Once they have 30 or so applicants in the pool, my guess is that they may draw candidates based on qualifications. (IE just because you got a yes letter first doesn't mean that you'll get called first.) Of course that's not based on any actual info that I have, more of a hunch.