I suggest your son check his admissions web page & see if his nom has shown up. Once they are submitted they are reflected on the web fairly quickly. Though your son got a letter notifying him of the nom, it does not need to be submitted by the MOC to the SA until 1/31 so it is conceivable that they don't have it yet, though typically the MOC would send the letter to your son concurrently to sending it to the SA.
The SA cannot award an appointment without a nom. However, having a nom & being QQQ does not guarantee an appointment. Each MOC can submit up to 10 nominees for every open slot at each SA. They can nominate less than 10 but they cannot nominate more than 10 (per available slot). They will submit their slate of nominees in one of three ways.
1) One nominee selected as "principal" & the rest in rank order selected by the MOC. In this case the "principal" will get the appointment unless they are not QQQ. If they are not QQQ (or turn it down) the others on the slate will get the appointment in the order designated by the MOC.
2) One nominee is "principal" & the others are listed randomly. The SA is to select the principal but if not QQQ (or turns it down) the SA selects the runner up based on the SA computation of the WCSs on the slate. The most competitive gaining the appointment.
3) All 10 are on the list randomly (often alphabetical) & the SA is asked to select the one they feel to be most qualified based on the WCS of the nominees.
In your sons case, perhaps the MOC letter tells him what type of nomination is given (principal with ranked alternates, principal with un-ranked competitive alternates, or as an un-ranked competitive list).
There are numerous other factors in converting the nom & QQQ into an appointment. I don't want to get too detailed and confuse you! Suffice it to say, however, that if your son doesn't make the first level, he will end up in the national pool & can still obtain an appointment from there, depending on his WCS. Because his WCS impacts appointments tremendously, it is always good for candidates to continue updating their files with any new information that may add points to their file. I know of situations where the difference between an appointee & a non-appointee was extremely small & an updated file made the difference. It always behooves a candidate to be certain their file is complete & any substantive updates are made.
A substantive update is anything from new test scores / transcripts to becoming president of a club or a new award. I know of people who updated files at the end of the sports season to indicate their teams achievement (1st, 2nd in league etc) or to add things that show some leadership in church activities or school ... many winter or spring sports assign captain around now and that would be an appropriate update. If a student decides to tutor others this is a leadership role & can be added (it should be more formal than sitting at lunch helping a friend with homework once or twice!). Providing verification of these items is good, too. For instance, if made captain, have your coach vouch for it and send it in, or have your pastor vouch for your integral role in whatever activity your organized etc. The number of things that may add a point here or two points there is phenomenal.
Good luck and let us know how it goes!