Luria Nova has in fact done several of those things. The Dragon King has been denounced, and Luria has declared its own monarch. Furthermore, why would anyone declare Paisly D'hara's de jure capital? Luria would recognize it as Port Nebel. Furthermore, Alanna Anaris has just as much, if not more claim on D'haran lands than the majority of the Nobility of D'hara. She conquered it, the Monarch of Shadovar passed without issue, and therefore, the conquering monarch would have claim by rights of inheritance. Luria may not exercise de facto control, but in the BM universe where the international law you cite has no relevance because it does not exist, it still exercises a de jure claim through right of conquest. Furthermore, if you look at the diplomatic dealings, that doesn't necessarily mean a nation gives up all claim on the lands the entity it is dealing with holds. North Korea and South Korea hold to an armistice, and both will tell you that the other half of Korea is rightfully theirs and both are to a degree, correct in this.
A lurian shadow government is an interesting idea...
