...And "unknown knowns" (model uncertainty?) that was never mentioned by Mr. Rumsfeld, at least not in that speech. 

I agree that Mr. Rumsfeld should have mentioned unkonwn knowns, ie situations where we don't realize that we know something.I generally think of these situations as ones where some part of an organization or body doesn't know that another part knows something. Sort of a left hand not telling the right hand problem. I have found this in my research when by chance I have found answers in the library to something I had been wondering about. The knowledge existed, I just didn't know that and hadn't been able to find it until I tripped over it while looking for something else.