To your point, it is a Letter Of Assurance (LOA).
The LOA is a
Conditional Offer of Appointment, which means that if you meet the condition(s) that are spelled out (Get a nomination, pass DoDMERB screening, etc) then you will
be offered an appointment. As
@mom3boys so aptly puts it - your goal is the appointment - not an LOA.
Very few applicants get an LOA. The Admissions Board will decide from time to time to grant an LOA based on a stellar applicant's nearly-complete application.
As I wrote before, there are precious few of these and they are only granted in cases where the applicant has scored at the top level in nearly every category measured, and/or in other rare cases is a stellar athletic recruit.
We are talking (and it's pure conjecture) about 100 to 150 applicants to the incoming class will receive LOAs. Since the other 1,000 or so in the class do NOT receive LOAs, it is not something to hang your hat on.
Complete the application. Put your best foot forward, and let the chips fall as they may.
There are applicants out there every year who receive full-ride scholarships to Harvard and Yale, who do not receive an LOA, or an Offer of Appointment, for that matter.