Exits are a stupid test for what they're trying to measure here. By that standard, Airbnb and Dropbox are failures. Exits are a reasonable test for investments made, say, 10 years ago. But none of the incubators are that old yet. So the right way to judge them is by the valuations of the startups they've funded. Unless the venture business as a whole loses money, that will be a lower bound on the eventual exit number…
If the startup is profitable and self sustain itself, does it count as success or failure?
To investors, whether an investment is a success or a failure is indeterminate till the company either goes out of business or returns the capital invested.