...Robin would have undoubtedly sent news of his occupation of those planets to Pythor, but only after they were completely occupied and defenses were set up, and this is to prevent Pythor from even thinking about returning to fight for them, this is technically what Pythor is also doing in the central and western regions of Nihari.
The first expected reaction of someone like Pythor would be to get angry and send part of his army to at least two planets... If he did this then Robin should have sent more forces to hold those planets to force Pythor's men into request support and open several major battlefields and spread the Great Serpent's army, and thus be able to return to Planet Nihari, or if they don't get support then he forces them to retreat and thus keep the nine planets for himself as a pressure card.
But in the end, occupying and defending these planets is not the goal, but the means to the next step...
