I was in session 1 last year and received my appointment to c/o 2021 a few months ago and you will see some things on the internet about how ss doesn't affect admissions. I can tell you pretty frankly that isn't entirely true
To avoid confusion -- the message is that lack of acceptance to NASS is not an indicator of your competitiveness for Admission to USNA. If you didn't get selected, it does not hurt your chance of Admission. NASS is first, and foremost an outreach program, trying to promote awareness of the Academy. Yes, I am aware that some view it as an opportunity to test the waters, see if they like USNA, etc. and even people from right outside the Gates attend NASS, but the main objective, from USNA perspective is outreach and awareness. If you didn't get into NASS..don't dispair , you probably aren't the target audience.
As to NPG's comment -- yes, the Squad Leader is going to evaluate you. How much weight such an evaluation is going to carry is not clear. Purely speculation on my part, but I would not expect that a Squad Leader evaluation would provide any significant advantage to the application process. Like the BGO interview, it is probably most influential at the extremes, and even then, other factors have much greater weight. In other words, if you got to NASS, are a complete stick in the mud, can't get along with others, and generally have a bad attitude, the Squad Leader interview could harm you, but I really don't think that even an outstanding NASS evaluation would elevate you over a similar qualified applicant that didn't attend NASS.