Re: Note that they didn't bother with open source operating systems
OpenBSD has been included in embargoed fixes before, and slipped the changes into the codebase so users were protected on day one of the public notice.
Pretty sure their history of doing that is why they WEREN'T included. If you slip something into the code repository, people can diff it and figure out what you're up to. They don't need a commit message that says SECURITY HOLE HERE to catch on.
Kinda by definition open-source projects can't keep secrets.