That's after accounting for the recent increases in student intake. All but the oldest seven have started in the last decade, and the older seven have also increased their intake by 50-100% in the meanwhile. So, as of a decade ago, the IITs would have been graduating ~2000 undergrads per year, all seven institutions combined. (The counting is a little complicated, but I expect that number to be less than ~3000 nonetheless)

That's the relevant number, since those who've founded unicorns can probably be assumed to have started their undergraduate education at least a decade ago. (4-5 years in college and then at least a few years working).