Just read on the forum pages at the Clemson Insider that DRad indicated not one game last year had the full allotment of student tickets distributed. Much of the blame has been on the students but I can speak first hand as my daughter could not get a ticket to every game, often time getting tickets on the after market sites. I think the new ticketing system is more to blame than the students. When I attended Clemson, you had certain days and times (based on class) to go in person to pick up your ticket, often time there would be lines. This new system makes it too easy for the students to get a ticket in case they want to go and the die hard student left without a ticket.
The way I understood DRad on Saturday, was that they never actually sold all of the tickets that they made available for students to purchase. I would assume those unsold tickets went back into the free allotment which were likely all distrubuted... at least for the bigger games.