If I interpret the summary from the 2022 Class Portrait correctly, there were 6,652 nominations and 1,373 offers of appointment which calculates to 20.6%. However, I would think that the number of nominations is higher than the number of applicants with nominations (as some applicants have multiple nominations) which would increase the yield rate.
Having multiple nominations will increase the number of times that applicant will go before the selection board, which is good, but I have not seen a comparison between applicants with single nominations and applicants with multiple nominations.
No. Having multiple nominations gives the academy some flexibility as to who gets charged with the nomination, but has nothing to do with whether or not you receive that offer in the first place.
Each year, there are approximately 3,500 candidates who are triple-qualified ("3Q") with a nomination. Of those 3,500, approximately 1,350 will receive an Offer of Appointment.
That's right at 39% - which are pretty good odds - but a long way from being a sure thing.