MoC have 3 kinds of "slates" they can submit to the academies.
1. Designate a Principal nominee with unranked alternates.
2. Designate a Principal nominee with ranked alternates.
3. All nominees are unranked.
As long as a candidate who was given a principal nomination is qualified scholastically, medically, and physically, the academy is required by law to offer that person an appointment. If that principal nominee turns down the appointment or is not qualified, then the academy would choose the next person on the list if the congressman ranked the alternates, or the academy would get to choose if the congressman did not rank them.
If the congressman did not rank any of the nominees to begin with, the academy gets to choose at least one of their choosing that is the most qualified.
To find out which kind of slate your senator used, you need to call his office. I don't know how to find it now, but about a month ago I saw a page on USAFA's site that said that 74% of MoC use a totally unranked slate, 14% designate a principal nominee with unranked alternates, and only 12% designate a principal nominee with ranked alternates.