[squarefoot]

> So there could be (and likely are) implementations out there which are fully compliant with the standard, but have not chosen to get certified, and are therefore technically still "not Unix".

I'm not sure about certification, as compliance was mandated by the US Govt so there may have been one, but Windows NT had its POSIX API layer which I used ages ago to port some Unix network code to it just by changing a couple lines. No tools or anything else, that is, one didn't have a POSIX shell or any usual Unix tool, but the way to say open a socket and initiate network traffic was pretty much the same.