I think you are misunderstanding the meaning of 'the cat is out of the bag', although I also think the OP misunderstands it, too.

The saying means that you can't un-tell a secret... once a secret is known to the public, you can't make it a secret again.

I think the more appropriate saying would be a similar, but slightly different, one: "That ship has already sailed"

That one is more about "it is too late to do anything about this" and less about information.