I have no real idea yet. But I'd want to distinguish between secrets in the hands of an informal or extralegal group like the Iran-contra conspirators, and official state secrets. Unofficial secrets are guarded only by the wiles of those who keep them, whereas official secrets in theory are kept that way by all the resources of the state. Also, there are degrees of secrecy - known unknowns and unknown unknowns, basically! An example of a "known unknown" would be nuclear targeting plans or anthrax weaponization recipes. We know they exist, we know they're on file somewhere, but we just don't know the details. An example of an "unknown unknown" might be the secret truth about the Kennedy assassination - the CIA might have a secret file containing proof that Oswald did not alone, or it might not. I suppose that some of the higher degrees of secrecy are all about keeping something in the "unknown unknown" category.
So let's distinguish two forms of position 2 in my list, 2A and 2B. According to 2A, the proof of the Iraqi connection remains outside official channels entirely, in the hands of a cabal. According to 2B, it is already in the keeping of the official guardians of secrecy, whoever they are; filed away as something above top secret.
Keep in mind that, unless all the perpetrators are dead, somebody (and almost certainly a group of people) is, in fact, keeping a secret. (This is true no matter who sent the anthrax.)
So your distinction between a cabal and an official group of some government could apply to any of the possibilities 1-5. And, of course, there isn't really a sharp line between the informal cabal and the official government organization, at least if many members of the cabal are government officials. Iran-Contra is a good example of this.