The 3Q letter for USMA is sent by the Regional Commander, so as some have said in prior posts, not everyone, even 3Q'd, may receive the letter -- it's up to the RC. The letter basically says "We have received all your application information and the Admissions Committee has qualified your file." It goes on to mention that all qualified applicants are placed on the a National Waiting List until appointments are made, and that most appointments will be tendered between {date} and {date}. The letter also reminds candidates they are still competing for admission and should continue updating their records with significant achievements.
Boymom73 -- your DS may have an appointment to USAFA, but USNA doesn't tell candidates if they are 3Q. Your DS could reach out to his USMA RC for clarification. Don't assume 3Q among the SAs, although if his stats are high in all areas, he probably is. Good luck!