#even the twelfth seat of squad 8 hasn't been there since he left

[troius]

How did Kisuke know everything about everyone to solve every problem but somehow only knows the vaguest of info about the right hand of the soul king?

I'm not saying he should know about Jushiro's condition but he should have at least known a wikipidia level of info.

Nah because something that is abundantly clear about Soul Society is that nobody in the Seireitei has the slightest bit of actual knowledge of Rukongai. And Kisuke isn't an exception.

Like, Soul Society is an incredible stratified place. All of the most powerful and important people are in the Seireitei. And even the powerful folks from outside are eventually brought in, because the temptation of power/a better life is much too high to resist. And so the Soul Reapers don't care too much about what goes on beyond their walls! Sure, they might need to kill a particularly nasty hollow now and again, or mass-murder the inhabitants to maintain the balance of souls in an emergency, but otherwise? Who cares!

Ichigo and co. jumped from the world of the living to Soul Society, but the Court Guards literally did not care so long as they were not in the Seireitei. Aizen was conducting crazy hollow research for years out there, and Kisuke hadn't the slightest inkling, because why would he? He's a retainer of the Shihouin clan! Their eyes are on their peers around them and the god above them, not the outside world that they consider beneath them.