It is also referred to as a "Land Patent." In short, it recognizes the sovereignty of the land-holder, a recognition granted by governments. If such a concept were legal in the framework of the Outer Space Treaty, it could mean the Treaty need not be withdrawn from.
Of course, it would probably be easier to withdraw from the Treaty. And it would probably confer onto Corporations the kind of power that is described in countless Science Fiction stories.
Even a charter corporation would do. A lease. Anything. The investors expect some kind of paper.