Sort of like the buyer or purchasing agent for a company. That person enters into contracts, but it isn’t a personal bond, it’s institutional, representing the company’s entering into a contract.
Either he knows it is correct, or he believes it to be correct based on others who he trusts. If the others lied to him, they are liable.
That's your point of view, but I submit it is not Rosenstein's point of view, nor is it the DOJ's point of view. If Roesenstine believed he was personally responsible for the contents, and in any way personally liable for errors within, he would have behaved differently.
-- If the others lied to him, they are liable. --
Are they? That seems a contradiction to your previous assertion, that Rosenstein is personally liable. Otherwise, you say, what is the point of him signing it?