The Navy has no such guarantee in writing, but often (not always) accommodated in practice.
Yeah in my (I think *our*) time, I never saw #1 not get what they wanted. Probably even the top 5 got what they wanted. It's been a long time, but 72 NSS seems to ring a bell for what got me there, and there were people with less who did too. It's probably in a post of mine from 15-16 years ago if any nerds want to go looking. But to be fair, I wouldn't say that making it through the T-45 advanced syllabus was a high point in my life......I still remember my check in meeting with the VMFAT-101 Training Officer, who did not mince any words when he looked at my jacket and said "statistically, you will not make it through our FRS"
