One of the possibilities I've been thinking about so far as Corvus knowing about Tamsy is that he knows, but isn't strong enough to do anything about it in a way that won't get people killed.
Corvus at a minimum has vague inclinations about Tamsy's true nature and the question right now is; Does he actually know that Tamsy is evil? If he does, why hasn't he done anything? The answer could genuinely be that Tamsy is by all practical means holding the cleaners hostage, and Corvus is the only one who knows that. Tamsy's introduction is one of the most harrowing parts of his character given what we now know about his intentions. He proved that he could easily take out the entirety of the cleaners without much issue, and he was holding back while he did it. This isn't even factoring in the book which we don't know the full abilities of on top of his regular Jinki. Tamsy is THE strongest living character in the series. God Mymo is probably the only one to properly surpass him and it goes without saying how much of a problem he was. Its could be why Tamsy seems to get so much leeway from Corvus. Going into the vault and taking the boots out without Corvus being there? No repercussions. Given vacations seemingly whenever he asks? No further questions asked. It's not a question of 'Is Corvus stronger than Tamsy', it's 'Can Corvus stop Tamsy from killing several cleaners and potentially civilians if he ever attempted to oust him?' and the answer is probably not.
















