But...I don't think they're doing that?
I... think they were? Fairly explicitly, actually. Current thread of discussion started with talking about not being aware of a possible latent bisexuality, that appeared to be at least partially caused by a previous conviction of asexuality. That'd be an example of an unknown known (the bisexuality, which the hormones et al were apparently pretty aware of) being suppressed by a self-categorization (the asexuality). It seems to be sliding towards a known known, but that previous categorization quite likely got in the way of it, slowed it down or delayed the realization, possibly by quite a bit.
And it's basically something we know but don't know we know, mech. A fairly mundane example would be an organization having a particular bit of data on someone tucked away in a cabinet somewhere, without anything else pointing to its existence. The organization has the information, they just don't know they have it. Another would be just stuff like test taking -- being unable to recall something, possibly even that you studied it at all, but then going a series of problems before being able to recall it again; the information didn't take a jaunt out into the aether during the interim, but you weren't aware of what it was. Biology, it probably comes up the most with sensory stuff, being subconsciously aware of this or that without being consciously aware. Unidentified gender identity mismatch is another fairly common expression -- the body/brain knows the problem, but it's not recognized. Stuff like that. Things you're aware of, but have no actual cognizance that you are.
Least if I'm remember everything correctly. I don't even recall where I last ran into something approach a formal treatment of the heuristic, so it's very possible I'm not.