I thought within canon Koubayashi Maru was basically step last, you take the test, they decide from that whether or not you’re really cut out for command and one way or the other tomorrow is graduation day. So there wouldn’t necessarily be a lot of time for upper classmen to ruin it for lower. How Kirk found out is never explained, except it’s pretty well stated that he was a climber from the start and good at making connections.
without going into a spoiler toooo much, supposedly kirk is challenged to accomplish something in X number of years and cadet kirk responds he will do it in x-2 years.
(something like that.)
The BIG SPOILER RUMOR is that there is some sort of temporal manipulation going on with regards to kirk’s life.
Thanks for the additional comments. Kirk had to find out about it from someone.