Re-reading Heir to the Dragon for the umphteenth time for data mining I realized that the Draconis Combine had never actually sanctioned the formation of the FRR or recognized the breakaway state in a formally correct way.
Instead, Theodore Kurita forged his father's (the Coordinator's) electronic seal in the electronic documents, with Subhash Indrahar watching via spysoftware, and sent the Combine's recognition to ComStar after the Coordinator had stormed out declaring he wouldn't sign those documents.
Now this is all water under the bridge now, with the timeline advanced way over a century beyond that point. The FRR was subsequently defended against "Ronin" forces by the Draconis Combine, was largely conquered by the Ghost Bears, its remnant officially merged with the occupied territories to form the Ghost Bear Dominion. Presumably, peace treaties between the Ghost Bears and the Combine in the aftermath of either of their two wars also have something to say about who owns which planet.
Or maybe not. After all, if the original forgery of the Combine's approval can be proven, it might be grounds for the Combine to claim the former Rasalhague District worlds as still belonging to their realm.
(If you assume that the Combine needs a legal excuse to go to war in the first place, that is - after all they've maintained for centuries that all worlds are belong to them anyways.)