27 wasn’t certified and 26 was listed but is now removed.
replyFrom that Wayback page, it looks like only one version of macOS is certified at any one time: the latest version. Since macOS Golden Gate was only recently released, perhaps it's a process blip and we'll see Golden Gate listed soon.
replyNope, Sequoia and Tahoe both remain registered: https://www.opengroup.org/openbrand/register/apple.htm
reply26 is in UNIX 03, if you use the pulldown
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