They probably had some nice checks written with their name in the "pay to the order of"... but they weren't the ones doing the selling, negotiating the price, or having any say in it more than any other shareholder (weighted by the shares and voting status) would.

To that end, with their various rounds of funding ( https://www.crunchbase.com/organization/stack-overflow/compa... ), they likely had very little say in any of it after that series E ( https://stackoverflow.co/company/press/archive/series-e ) which is after Jeff and Joel had left and likely diluted any value they had substantially.