Yes, the title can be combined in any fashion. This will be a short post explaining how, with the three traditional combinations first, then the fourth, Unknown Knowns.
This is simple enough, and should, hopefully, be the basic of any plan. It means something that you know you know, essentially a truth that you know about.
These are also integral in the making of a plan. These are the variables you cannot predict--whether because of insanity, lack of information, or anything else. In other words, it is something you know you do not know--so you can prepare for it.
These are the things you simply cannot prepare for. There is something that could mess you up or help you, but you have no idea it exists. In short, you don't know what you don't know.
Here is where I get the most odd looks. This is fair, since the only reason I thought of this was because I imagined known/unknown knowns/unknowns as a chart, the former on the top and the latter on the side. What is this? This is something you should know, something you either have been told or have learned, but you do not remember it. Put another way: it's true, you would recognize it, but it doesn't quite make it into your head when you're planning.
(As a side note, something I found while spell-checking this: My computer recognizes known, unknown, and unknowns, but not knowns. Weird.)
Tropes for planning (Warning: Addictive):
And when you figure everything out quickly: