[rlucas]

Pro-rata doesn't mean what you are implying.

Pro-rata is in theory the right (but not the obligation) to buy back in, at the new price, to get back to your prior ownership level.

In practice however, pro-rata is a firmly stated polite request to the next round lead investor to let you do so. The real determinant of whether you get to use the pro-rata right is whether your next round lead investor is OK with it (and whether you want to try to block that next round).

[dataisfun]

Yes, I know. But if you want to tell YC they don't get their pro rata (or practically speaking, convince the founder to tussle with them over that), have fun. I've seen them not budge even when it makes the founder's life much harder as they struggle to balance the pretty typical ownership requirements of new money.

[rlucas]

Good point, YC is a uniquely powerful market participant these days and has both the power and the breadth of portfolio to negotiate hard.