The paper value of their stake is still 6.5M. The paper value of Facebook as a whole (the market cap) is now 20B higher than it was prior to that trade, if you

The paper value of their stake is still 6.5M. The paper value of Facebook as a whole (the market cap) is now 20B higher than it was prior to that trade, if you take that share price as the new share value, which is what Forbes did, and what 37signals objects to.