Zulu, I hate dragging this out.
Firstly, I apologise to all for the tone of my previous posts. Unnecessary, and the fruit of tiredness, a bad day, and the provocation of a personality-lacking poster called Someone.
Back to the question at hand, correlation is an interesting concept when discussing the relationship between two VARIABLES (we all knew that? good!). In your scenario, you are talking about success at AC, hence 1st-round success is no longer a variable, its a given: everybody at AC has passed the first round.
Furthermore, and following up on the wise comment by Mars A Day, once you get to AC, you have a clean slate compared to all other AC candidates. You have all passed the 1st round, and that puts no one at any advantage. So, forget about correlation. It's a poor and misleading term.
Furthermore, if I came on here and replied "there is a correlation of 0.28 between success at 1st Round and AC", how many people do you think that would mean anything to?
What you want to know is how many people do they invite to AC vs how many they want to see pass through the AC.
I see many people use "fancy" terminology like correlation, when it is really uncessary, just because they think it makes them sound smarter. Maybe I jumped on your post due to a backlog of frustration due to that. Might not be your case. No offence intended mate.