It would easy enough to look through the old forum posts, but just based off memory, I would say that roughly 1/3 of those advancing out outside the top 24. But in many cases, a bunch of players ranked 25-30 fall within that 1/3 number.
A better question is how many outside the top 30 make it to round 2. And again, based on memory, this number is usually in the 20-25% range (4 to 6).