Assuming the MOC submitted a list of 10 candidates (and not a single name) it means they all got nominations. The NA picked one from that list to offer an appointment. She turned it down so there are 9 others who can take that slot - at the discretion of the NA. In that case, the Mid would count against the 5 each MOC can have at the NA at any one time. If OTOH, the NA chooses not to pick one of those remaining 9, a slot opens in the class and can be from any district. That Mid would not count as one of the MOC's 5.
Do the math: in CT we have 5 MOC and 2 Sen = 7 slots (assuming they each have one opening) yet there were 19 or 20 plebes my DD's year. So 12/13 were nominated but did not count toward the 5 each could have attending.
I also think you're confusing the national pool with the wait list. The pool is all those candidates 3Q's with a nomination. It's from those that the class if filled out. (Math again: 435 MOC + 100 Sen = 535 Mids. Say the other nom sources = 400 (pres, vp, NAPS, foundation, fleet) 535 + 400 = 935. Class is 1220 so the other 285 come from the national pool. (All number made up for illustration.)
The wait list is (probably) a small number of candidates to whom the NA will offer an appointment in the event someone already in the 1220 declines at the last minute.
