Occasionally it’s the public market…
https://medium.com/@Arakunrin/the-post-ipo-performance-of-y-...
Most often for successful exits, it’s to get acquired and shut down the original product with a “Our Amazing Journey” blog post.
For instance, I know Coinbase may be down -22% from the IPO price, but that doesn't mean YCombinator lost money nor made very little. If they, for instance, sold off during the first few days of the IPO they would have made out quite well.
There's also the whole question of how much money did YCombinator put in vs what they got out.
Without knowing this, about all the chart tells me is YCombinator is not a predicated on building exceedingly durable businesses, but it doesn't mean they lost money on any of these investments either.