Might have been true at one point, but I agree with Vellos. If you conduct negotiations and recognize them as a sovereign entity, then you've legitimized them. Doesn't mean you can't ignore all that diplomacy treating them as a real and rightful realm, and beat the war drum with "they be rebels". Just, OOC you have to admit that Luria dealt with them not as rebels but as a true and proper realm.
You can make treaties with a realm that you believe is made up of rebels illegally occupying lands that are rightfully yours. Just because they are recognized as a sovereign realm doesn't mean that you recognize everything they do or all the lands that they claim.
D'Hara holds lands which Luria lays no claim to.
