I believe it's a mixture of candidates with/without LOA's. I sent in my completed application back in the fall and received an offer of appt soon thereafter, but never got an LOA. I actually had a Presidential nomination but no congressional nom. Most of those who receive LOA's are just waiting on the nomination.
I'm pretty sure USAFA is sending out appt packages to candidates w/o LOA's by now. There are several guys and girls at my school who never received an LOA but have received offers of appt, including one girl who got into West Point two weeks ago. I'm not sure of USMA's policies on LOA's, though.
Best of luck to your son, pos2013falcon. (I read your introduction.) Did he attend Summer Seminar? If he's a two sport-athlete with enough academic/extracurricular/leadership credentials, hopefully the mailman brings good news in the coming weeks!
Out of curiosity, what state do you live in? There's a USAFA appointee at my school who wrestles and is going up to Sectionals soon. If you live in Illinois, maybe they've met.