> It seems basically impossible for everyone to have overhired, for the simple reason that qualified workers do not appear and disappear from nowhere. There is a population of qualified workers in the software sector, and only new grads and retirement can move the needle significantly.

SWEs (and most any role for that matter) definitely can be minted in ways besides graduating with a relevant major. On top of that there's also H1Bs and contractors. Plus "overhiring" doesn't necessarily just mean absolute headcount, it could be compensation, scope, middle managers, etc. The definition of "qualified" is also malleable depending on the incentives.

> So, if someone overhired then someone else must have done without, all things considered.

Beyond the previous points, this also assumes the supply of labor is independent of the demand, and it's clearly not. As the demand increases, so does compensation, outreach, advertising/propaganda, etc. Everybody can overhire simultaneously as a result of pushing for growth of the supply of labor.