I'm sure they could, but it's not really relevant. It's more about the 2-3 Dropbox, AirBnB, Heroku like companies.

Think of it this way with Heroku:

YC gets 6-7% initially and probably ends up with close to 3% after Series A and B. That's $6.2M on the $212M exit price.

A single exit like Heroku returns them enough to run YC for at least a couple years and returned >10x for other investors.

So while you could show that, it doesn't really matter to YC or to investors, because they have those 2-3 huge wins.