How many startups needed to but were unable to raise capital in successive rounds? If the failure rate of successive raise attempts is low then I'd suspect that the driving factor would be the desire to raise capital.

Given that we've been in a record bull market for nearly a decade and there are signs of slowing, it may be hard to extrapolate these findings to the future. It would be interesting to try to model what things would have looked like on this data set at lower levels of investment. This type of information would be hugely valuable if there is an investment regime change occurring.