Matty -- While what you say appears to be "technically correct" (have seen this advice on "help with recruiting" websites), I didn't see this clearly stated on the NLI website. It probably also depends on what the Academy's practice is regarding players that sign an NLI. I couldn't find anything clear on-line from USAFA but did find the following from USNA's website, it appears they respect the NLI:
http://www.navysports.com/compliance/navy-compliance.html
"National Letter of Intent
While the Academy doesn’t subscribe to the National Letter of Intent (NLI), other institutions you may be considering do. You may get information on the NLI by
visiting their website. Once you sign a NLI with an institution, you are bound to that school for one academic year."
If your DS isn't going to play a NCAA sport at USAFA, it may not matter. If he is, in addition to USAFA admissions, he might want to contact the appropriate USAFA coach to see where he stands and to get some advice. Best wishes.