There’s regulations around the 409a valuation of the company, it’s not completely based on the unicorn fairy dust that VCs use to value a company. Admittedly 409a valuations are far from perfect for many reasons, but they aren’t the same as the valuations you commonly hear when a company closes a round.

It adjusts to the price on that day far in the future when employees get out of lockup, but if it spans tax years you're still screwed. Basically, when you have gains, you only ensure realistic taxes when you exercise and sell within the same tax year; otherwise you take a huge risk.