But if pioneering discovery is your basis for sovereignty, then it's likely it's the the Ba'ku's planet.
We have no idea when the Rommis or Klinks stumbled upon Klach D'Kel Brakt, but it's not crazy to think it was after 2066. If both races are supposedly on a similar technical evolutionary trajectory as humans, we have to figure they were still, cosmically, infantile. This was only three years after Cochrane's flight, after all. Also, all non-canon references depict KDB as being some considerable distance from either Romulus or Qo'Nos.
The only other events we have to go by are the Augment coup was wasn't until almost a century later and the conflict which was in 2271.