I would guess the vast majority of term sheets have a clause in them that says something like if you sell your shares pre-IPO then every shareholder of that class has to have the option to sell their shares with you on a pro-rata basis and buy the shares on a pro-rata basis, along with a bunch of other restrictions that make it basically impossible to sell any employee stock option/grant shares before a liquidity event. They sometimes make exceptions for senior people so they can move out of their studio in the East Bay to a 1 bedroom closer to the company (or other "quality of life benefits the company" type reasons) but that's the exception. I would think the VCs would basically lock this down going forward starting with all future first round term sheets because the last thing they want is insiders becoming less committed by diversifying away from the company, not to mention having to convince a bunch of random shareholders of whatever direction they want to take the company in. They're pretty pathological about wanting pigs not chickens.
Does that include non-key employees like programmers, etc?
One of my wife's friends cofounded a company (one you would know) that got sold. He had left years ago but couldn't cash out until then. They were relatively cash poor and income poor but were worth a lot in paper - that there was likely a buyer for.
