Two of those programs predate POSIX and do not indicate that OpenBSD follows POSIX.

They are making their operating system to the design they like best. Some of it happens to coincide with what POSIX asks for, but it is merely coincidental.

I vaguely recall some interview with or blog post / talk by an OpenBSD developer, where they said that POSIX tended towards adopting whatever GNU/Linux did, and that the BSD crowd's interests were not taken into consideration that much.

I don't know much about the process behind POSIX/SUS, but I can understand how OpenBSD developers wouldn't be super enthusiastic about POSIX compliance if they felt their input was falling on deaf ears.

FWIW, I did use the SUS as my main reference when writing a few hobby projects, and OpenBSD gave me no problems whatsoever. macOS, on the other hand, which is a certified Unix, did not support barriers at the time (that was ~10 years ago, I have no idea if Apple added support since). (I know barriers are optional, but come on.)