AFROTC usually graduates about 1200 people each year and usually recieves 400-500 pilot slots (last number I heard).  The number of pilot slots differs each year, according to the needs of the AF.  When you select what track (fighter/bomber, heavy, helo) and when you select which airframe, the numbers are, again, based on the needs of the AF.  Sometimes there are quite a few fighter slots in UPT, sometimes none.