[Stratoscope]

Not all shares are the same. Corporations have different classes of stock: as a simple example there may be common stock and preferred stock.

In a "liquidity event", and especially in a "down round" where the company is bought at a lower price per share than previous investors paid, those shares are not treated the same. Preferred shares may get something from the new investment round (perhaps less than they invested), while common shares may have their value wiped out to zero.

(Source: I have been a "commoner" in a company that was bought in a down round where my stock was zeroed but the preferred shares were still worth something.)