Shouldn't you, as the student, be given something, anything to know how you are doing before the very end (other than your ATS at the end of a flight). People can say, "work as hard as you can and you will get what you get" till the cows come home, but imagine going through all of high school not knowing if you had the grades to get into Harvard or the grades to go to a crappy college. Then imagine going all through college not know if you were strong enough to get a top job in the sector of your choice, or go to the grad school of your choice
I guess I wasn't quite clear enough in the original post. You want to know how well you are doing? NSS does not and can not tell you that. NSS just tells you what your ranking is in a class when you are done.
Why can't you know what your rank is at any given time? You used going through high school or college as an example. I wonder if you knew exactly what your class rank was during any given time while you were in high school or college. There are some high schools that can provide that at the end of each semester, maybe. College...not likely. What you did get every day while going through school was a grade for tests and assignments and a final grade for the course. Getting an A on a test doesn't tell you what your rank is or is going to be in your graduating class. Getting an A in a course doesn't tell you what your rank is or is going to be in your graduating class. It does tell you that you are passing.
So, what happens in flight school? You get daily grades on your exams and tests. Getting a 100% or 20 above MIF doesn't tell you what your rank is or is going to be in your selection class. It does tell you that you are passing. In fact, passing your flights tells you you are passing.
At the end of each Phase (API, Primary, Advanced, FRS) you will find out what your rank (NSS) is. Just like when you finally graduated from high school or college.
Maybe as a college freshman, you finished your first semester with a 3.9 GPA at a school where the average graduate finishes with a 3.0. So you figure you're near the top of your class, right? Not so fast. Your first semester was filled with classes like algebra. Just about everyone gets high grades there. What about when you're in your senior year with applied astrophysics? Will you still be getting that 3.9?
OK, maybe you just look at all the students who finished the semester at the same time. The average GPA was 3.8, so you're above average and on your way to "jets". Wait. Turns out all those students are on a 3 year program and you're on the 5 year program. You won't be ranked against them when you graduate. 4 1/2 years later, you look back to compare where you stood back then against those you finally ended up graduating with and it turns out the average was 4.0. So you were really below average. In fact, everyone but you had a 4.0, so you were at the bottom of your class and would have had a 20 NSS... if it could have been calculated.
Starting to get an idea why it is impossible to tell you what your NSS is after solo or starting forms or pretty much anytime before you select? Any number anyone gives you for an NSS before you are done has as much chance of actually being your NSS as winning a couple Lottos in a row.
This also should start to answer your second question as to why the ratio for a 50 NSS changes. When you were in high school, did you know what your class average GPA would be when you graduate? It probably ended up being pretty close to the classes that graduated a few years before you, but maybe very different from those that graduated decades before you.
It is the same in flight school. The average score of those selecting changes. It may go up. It may go down. Therefore, the average ratio that is equivalent to a 50 NSS changes.
Plus, and I'll dip my toe into some stats here, just as the average can change, the standard deviation of scores for a class change as well. +/-1.5 standard deviations from the average is a 65 and 35 NSS. That means that the scores for 65 NSS and 35 NSS could change even if the average score remained the same.
One last time...NSS is not a measure of performance. It is only a ranking within a specified group of people. The measure of your performance is the individual maneuver grades you get from the IPs.
How do you know if you are not passing? Maybe more appropriately, how do you know if you are on the road to attrition? Your IPs will let you know. If an IP in your chain (onwing, flight leader, student control, ops, XO, CO) hasn't cornered you and said, "get your ass in gear," you are passing. But basically, if you have more than a couple UNSATS, especially if they are consecutive, you should be concerned and better have your ass in gear.
So, the guy in the class ahead of you had a ratio of 1.2, was the top of his class and got jets. You've only got 4 flights left and have a ratio of 1.5. You tell your landlord you're moving, break up with your Pensacola debutante girlfriend, and start packing boxes. But then on selection day you find out there's only one jet seat your selection week and its going to a retread NFO (transvestfo) who has a 2.9 ratio. All the other seats are helo. Now you are homeless, have a psycho chick out to kill you, and can't find the box you put all your porn in. Did you make a good plan? Could anyone tell you it was going to happen? Did your NSS make any difference?