Maybe I'm being pedantic but as far as I can tell that document doesn't say when a SIGKILL can or can't be issued. So it seems like it would be valid to issue a SIGKILL at any time the kernel wants. Obviously, that's probably not users/programmers want but it seems to technically meet the specification you list.

Ah yes that is fairly clear, thanks, I was not able to find that. A plausible interpretation is that the kernel still reserves the right to terminate the process at anytime, including immediately after a general protection fault. Still an unexpected behavior, much like the Linux OOM killer.

2017? Wiki says macOS are UNIX 03 certified ;)