Usually, being the historical facts by definition simple mere brute facts, I don't see a particular reason to reserve the knowledge of them only for the insiders. Their knowledge is public domain. The knowledge of the religious meaning of mere facts is rather a top secret matter.
From the other hand, the same Roman penalty of crucifixion is designed to work as a public warning. The Romans couldn't care to hung up someone on the cross, if their goal was not, from the beginning, to show the victim to the highest number of observers there around.
Hence, in virtue of these two reasons, it is a priori improbable the idea that the knowledge of a historical Jesus was a top secret matter for Paul & readers.
In some cases, the silence about the historical facts is required by embarrassment. I think that Paul is really embarrassed about the way by which the his crucified Christ is interpreted by the not-Christians: as a historical crucified seditious.
In addition to the real embarrassment about the outsiders's interpretation of the "crucified Christ", Paul is not embarrassed about the fact itself of the crucifixion, which makes it highly improbable the historicity of Jesus. In the Paul's case, the embarrassment emerges when a esoteric knowledge (of the "crucified Christ") becomes, in the eyes of the outsiders, a human too human knowledge of public domain.
The same process will work later in the case of resurrection. It is a esoteric mystery, for Paul. But it ceases immediately to be such when:
- It is interpreted as a carnal resurrection;
- It is interpreted, even worse, as the banal theft of the corpse.