I recommend you read the nomination thread ‘stickies’ in the nomination area of this forum. There are lots of nomination 101 info there.
The answe is it depends. A MOC can submit a slate with anywhere between 1-10 individuals for each opening they have at a SA and wish to fill. They can submit a competitive slate, ranked or principle. The stickies mentioned will break this out in detail. A candidate must be 3Q to be offered an appointment. So even if a candidate comes in as #1 on a slate if they aren’t 3Q they won’t get it. They would then go to #2 and so on. Ranked slate sort of speaks for itself. Unranked is a MOC submitting 10 names and USNA picks. Generally WCS wins that. Principle is like ranked in many ways. Basically a MOC says this is my guy/gal and as long as they are 3Q they normally get an appointment per congressional code. USNA is slightly different as they are not a part of this congressional code, but in most cases USNA honors this.
So long story short... it’s not as simple as they pick one. Nomination process is separate from admissions. Admissions determines who is 3Q. One must be 3Q and have a Nom to be appointed. And yes theoretically if no one is 3Q on a slate, they would not offer an appointment that year.
Read both of these links that are "stickys" on the Nomination forum:
My apologies, I am new here.