New valuation data from PitchBook suggests that more than one-quarter of VC-backed "unicorns" have lost their horns, even if still being marked at more than $1 billion by their venture capitalists.Why it matters: Most limited partners aren't able to access top-decile firms. If they conclude that there are better investments elsewhere — such as passive indexes without high fees or illiquidity risk — that's where they'll go.The losers would be a generation of emerging VC fund managers and the foun...