archive.org suggests that What-If #31 appeared sometime around the 10th of February, 2013. That fits with one of the links in the article which first appeared (again, according to archive.org) in 2008 and ceased to be valid around 2015.
Randall has (or his team has) updated the formatting on the What-If site, but they haven't bothered to fix the links.
The irony here, I think, is that many people will have actually put together the chair they use to sit in front of their computer.