They are not actually over enrolling, unless they go above their allotted class size. They are over accepting, and then hoping that enough people drop off to get to their target enrollment.
This has worked for them the past few cycles, as evidenced by the fact that they did make a least a few calls off the Highest of the HPWL, and never asked anyone to defer, but they are playing with fire by utilizing this strategy, because, if they miss, they will have a problem on their hands. I just don't think they are doing it intentionally, because, if they were, they wouldn't be sending out the e-mails earlier in the cycle that now have
@Princeton Medical Student rightfully bent out of shape.
I think they just keep foolishly thinking their yield is going to drop from one year to the next, and, as a result, end up over accepting by more than they should, which results in them hitting their desired enrollment number with very minimal WL movement.