Well, the links you pointed to are for fairly old versions of Windows, and they are on a pirate site, rather than any old site that chooses to host them in the US. Is Mac OS there in its entirety? How about Oracle? DB2 from IBM?
Look at the availability of Linux source code compared to Mac OS X. It's everywhere.
In terms of proof and evidence, no one can really "prove" anything without actually experiencing the counterfactual world. You can't prove that MacOS X code would not be everywhere, for instance, just as I can't prove that it would be.
The best we can do is look for evidence that suggests how things might go.
Yeah, it's certainly working fine:
https://thepiratebay.se/torrent/7087027/Symantec_Norton_Anti...
https://thepiratebay.se/torrent/4149808/Windows_NT4_source_c...
https://thepiratebay.se/torrent/3497574/Windows_2000_source_...