142 on LinkedIn - guessing whatever number you found is inflated by people working in clinics that do Theranos tests or something along those lines?
Maybe LinkedIn doesn't capture every worker? You think they have greater than 30% penetration into the market?
I've actually had the (dis)pleasure of doing a fair bit of work in this area and have found LinkedIn to be pretty directionally accurate - for tech companies, I'd ballpark it at closer to 80-90% in most cases. They may very well be one of the outliers - I typically saw that in businesses structured in a way that made it readily understandable (ie 75 core employees, but hundreds of hourly warehouse employees without LinkedIn accounts). Not sure if Theranos has such a structure - perhaps the medical/research side is much less likely to have LinkedIn accounts than the tech side.