Earlier quoted context omitted.
The s1 listed 50m shares as coming from existing share holders but they did not break it out. Usually that is employees with vested shares and occasionally other investors. Was more common in the dot com IPO's but Zynga did that too as I recall
Ah ok, so the company makes an exception to the lockup period for IPO participation? How do they typically decide who gets to participate?
It's not an exception to the lockup, they are sold as part of the IPO. It's like taking money off the table in a VC round. Broadly speaking shares can come from three places when they are sold: new, which causes dilution, allocated but not granted, which is where the majority of employee grants come from, and finally vested ownership that is held by individuals. An IPO will have some mix of the latter two almost always. The relative proportion signals how bullish the insiders are to future prospects for the stock.