So no loops yet? I imagine things would get pretty exciting if the Commonwealth discovers a warp point into a system claimed by the Terran Union, or vice versa. With no ships or colonies in the system, proving prior discovery could be a bit tricky.
Me, I think that people should have sensor buoys of some kind that they can plunk down in systems. Buoys that can store messages for later visitors, in case the exploring force decides to explore a new system before reporting their survey data back.