dzn, some info from posts a couple years old on this italicized words not mine.
USNA National Pool
West Point uses the term "National Waiting List" and USNA uses the term "National Pool". They are one and the same. These are qualified candidates who are not the vacancy winner for their nomination. Candidates in the National pool did not receive any notice that they were in the pool-they just were as fully qualified non-slate winners.
USNA Wait List.
Later on in the spring - some USNA candidates may be notified they are on the "Wait List". This is a very select list of candidates who may or may not be called depending on last minute appointees canceling out.
From what I've read on previous year's threads, these candidates received a letter letting them know they had been placed on one of three wait lists, USNA, NAPS or Foundation.
I have read that they sometimes take as many as 50 from the list, sometimes none so it really depends on the number of class slots, appointees that accept and if they need to fill any vacancies in the class.
There is no mandatory number of appointees that must come from the USNA Wait List.
If we are fortunate enough to get on it at this point, DS would probably re-apply next year as that means he is/was very "close" to being a direct appointee and he would work with his RD to identify that area of his application that kept him from crossing the direct appointment threshold. Of course, that depends on how well he's doing at plan B and if he wants to leave there or not!
Good luck!