You're right, it's too low, see link at bottom: my guess is the $2B number, inclusive of all granted but not vested, is the correct #.
In general people way overestimate the # of SWEs at Google relative to the employee #, even within Google.
I don't wanna get too cute in public but some fermi estimates including, say, number of employees per engineer at a 100 person startup, and a jaundiced yet correct view of how much is outsourced at a company with a lot of grunt level SWE work common to every company, bridges the multiplier from there.
https://www.sec.gov/Archives/edgar/data/1364742/000156459021....
