The NWL is a misnomer. Exactly because of the nominations but also because admissions can fill the class not sequentially.
First, Rolling Admissions is filling appointments whenever they come available (say a presidential or MOC nomination arrives in October) and the director decides to award that appointment then instead of waiting until more test scores arrive and more candidates finish their application. Pro- solid individuals who complete early are likely to be appointed. Con - the best candidate may emerge over the course of the application process and not get in AND might not be strong enough to win a national vacancy.
Without rolling admissions, admissions is waiting longer to make sure the right individual wins a competitive slate (this is where the first/second waive talk comes in). They don't necessarily have to wait until file completion to know or accurately estimate IF
1) Admissions determines that the individual will most likely earn one of the top 150 spots off the NWL even if someone else emerges in the district. It's a pretty consistent WCS threshold every year. Much like SLE selection or selling airline tickets, a certain threshold is established and appointments are offered. As it comes closer to the file completion deadline and there is less variance in final WCS (the actual 150 threshold becomes clearer), more offers are sent. Similarly, there are thresholds for the service connected nominations as well.
2) The RC is likely to ask directly what each competitive candidate in the district is planning on adding. If they know #2, 3, 4 etc aren't taking a test and have no activities to update, then they can safely assume that #1 is going to win the vacancy.
Between all the nomination types (think separate lists for each MOC, service connected) that have the same candidates on multiple slates plus the NWL top 150 spots, appointments are not dolled out sequentially. The academy isn't just filling principals and LOAs first, then MOCs, and so forth down to the last 150 that somehow remain at the top. It is all happening at the same time in an ordered chaos that is just visible inside the admissions department.
The MOC have the option of using as many of their 5 vacancies that they have available at any time. If they want to use two vacancies and only nominate 3 people, that is their prerogative. That 3rd person will go on the NWL and compete as above.
Going back to the airplane seat sales, admissions will "oversell" appointments expecting a certain number of declinations on or before 1 May. Therefore, #1 may decline, but #2 won't get an appointment because there is already someone else from that district that has accepted their appointment and the class is "full", so admissions will use that individual to fill that vacancy. Again, this is all part of the ordered chaos. Rules of the road: 1) finish early 2) always seek ways to update/improve your file through the deadline, 3) be ready (until you get that TWE) even though someone from your district may already have been offered because their are always weird ways/times that people get in late in the cycle.