Part of the problem is that game shows themselves sort of defy the traditional understanding of what a cold open is. The Merriam-Webster definition is "a scene of a film or television episode that precedes the title sequence or opening credits and that typically takes place in the middle of the narrative or plot."
So, ignoring the scene and narrative parts of that definition, that would mean the late-stage Garry Moore TTTT open sort of defies a category. Because you see the title card first, without the announcer ever giving the title, and the subsequent introduction of the stars is equally blurry, since Garry says the title to kick it off and there's no superimposed logo. (Yes, the logo was superimposed at that point in the "mod" set years. I'm aware.)
Nickelodeon Double Dare and that Clue Crew bit could count by some interpretation, because both of those things precede the proper introduction of the show's title. Knockout's cold open is closest to how we generally understand it in scripted, like the opening scenes on The Office. No music, no titles - nothin'. But then Knockout never has a proper title sequence that follows. C'est la vie.
-Jason
