The USNA recommendation for % completion for doing interviews is 50%. That said, it is very BGO dependent. In all honesty, some don't have full-time jobs and/or only have one or two candidates in a cycle. They may well decide to interview everyone regardless of completion percentage.
For those who work and/or may have 20+ candidates in a cycle, it's simply a matter of time and prioritization. In my first years as a BGO, I would interview everyone as soon as they requested the interview or even seek them out. In many cases, the candidate never completed his her/package (not because of the interview
). When I'm looking at a potential 20 interviews a year, I realized I was "wasting" a lot of time on folks who really weren't interested in USNA.
Given limited time, I'd rather focus on those who have completed a high percentage of their packets -- including at least something THEY are responsible for (i.e., CFA or essay vs. their teacher recs). This tells me they are invested in the process -- they have enough interest to turn in most of their items.
I have made -- and continue to make -- exceptions, such as candidates who are looking for guidance/info about USNA in trying to decide if it's for them, etc. But where I live, those individuals are few and far between.
My personal view is that 100% is a bit much -- however, I must admit it's annoying when I interview someone at 89% and they never send in that final item.
At the end of the day, USNA won't review your packet until it's 100% complete. We were told that, last cycle, no one who didn't complete their packet was offered an appointment. So, provided your BGO is fairly prompt in scheduling interviews when you're done, there is minimal delay in USNA reviewing your record.