When a candidate is mathematically eliminated from the competition, then a TWE is sent. For a demonstration in simplest terms, let's say a candidate can only have one nomination from a MOC. That MOC nominates 10 individuals, and sends a competitive slate.
#1 will get the offer if they become medically qualified.
#2 gets an offer in this case because their WCS is high enough for NWL, but they have not accepted because USAFA is their priority.
#3 is fully qualified and waiting on one or both of the above to decide
#4 and #5 go to the same school. #5 is a recruited athlete with a LOA, so both 4 and 5 get an offer (too easy for #4 to lodge a complaint of why their DS or DD was better and didn't get an offer)
#6, and #7 get QNS because there is no way with all individuals above them with offers accepted and pending that they will fill that vacancy
#8 is DQ'd already because of academics
#9 is coming from USMAPS and will get an offer towards April
#10 didn't even have an application open because they didn't understand the process and West Point gladly closed the file they failed to complete in the month from the time the nomination came in and file deadline.
West Point will hold off on sending a QNS to #3 until they can make the determination who will bring the most to the class...a lot of that revolves around #1 and #2 obviously, but also the rest of the class in comparison to #3. Likely scenario:
April 15th roles around and #1 is not medically Q'd, then that vacancy would go to #2. Even if #2 declines because USAFA came through, #3 may or may not get an offer depending on how the class fill looks at that point in time. If it is full, #4 fills the vacancy, and #3 gets a QNS. If #3 is close to being a NWL candidate or fits a scholar or leadership class composition goal that is lacking, they may get an offer. With three accepted offers already, this district is on the high end of their proportional share of cadets for that class. Depending on the skill of the RC to see how the class fill and composition is shaping up relative to that #3, the RC may not even wait until the resolution of #1 and #2 to send the QNS. It is even more complex with multiple nominations with different candidates on each/multiple slates.
This is the art side behind filling a class that you do not see. If you are 3Q with a nomination and waiting on an offer, this is what is going on behind the scenes. The longer it takes to get your QNS, the closer on the bubble you are to an offer (for NWL, your MOC, or an additional appointee spot if you fit a class composition goal). At this point with almost 800 accepted, and 200 Prepsters still to be offered, most of the spots are filled or pending for this next class as we can safely assume that there are offers out for a significant portion of the remaining 200 spots. Given the number on this forum waiting on a med waiver or another service academy to make a decision on an offer, that number of available spots could quickly diminish in a matter of weeks/days as other TWEs come in and med waivers are approved. It could go the other way as well with med waivers not approved and offers from other service academies leading to declinations.