Actually, there is no "national pool." The Academies can only appoint from the individual nomination slates. Each member of Congress can have five people in the Academy at one time. So every year one or two slots open. If you are the number two in your slate and the number one accepts an appointment, and that congressman only has one slot, by law, the Academy can not put the number two person in. Even if they are more qualified than a number one from a different slate. Bottom line, you have to get in from one of your nomination slates. There is no "fill in the blank" process at the end to give out the rest of the slots. If there are slots unfilled, it is just a smaller class that year.
This is totally incorrect. Technically their are two different pools that are authorized.
Generally how a class is formed:
MOC Openings. 650 (Assuming 20% a year have two slots)
Presidential: 100 (Sons & Daughters of career service personnel)
Service Connected 200 (Active Duty, ROTC, Army Reserve, National Guard)
Qualified Alternates 150 (This is what is generally called getting in from the NWL. The next 150 applicants by OML are offered.
Additional Appointees The delta between the those offered above and the size the class needs to be. The academy can chose between any qualified candidate without regard to the OML. This is typically where LOA holders, Prepsters, recruited athletes, Foundation Scholars, Diversity Candidates get slotted. The only requirement is a 2/3 to 1/3 ratio between Congressional and Service Connected nomination holders.
Their is exactly a fill in the blank process at the end of the cycle. The class size is determined based on the overall strength of the Brigade/Corps of Cadets. They want to fill the class each year because attrition will always reduce the numbers.
Keep in mind that the process is not linear. They do not go through each line and move to the next. It is all happening at the same time.
So why would getting placed on the waitlist mean anything at USNA? (Note that it is not the same thin as people refer to as the NWL. This seems unique to USNA. USMA does not do this step) It is more likely that you just missed one of the slots above and someone may not accept in the coming weeks. The flip side is just because you were number two this year does not mean you will be number 1ext year. You have to keep working hard.