[As annoying as it is to have Matoba condescend to him about something as basic as the weird flow of time in ayakashi realms, as if he's still a green teenager showing up to an exorcism with his school bag stuffed full of supplies from the storehouse, it's at least confirmation of what he had suspected. So Matoba has been playing this "game" for quite a while...

He keeps his face at dismissive exorcist neutral, but he can't stop his eyes from widening in surprise once Matoba explains just how long 'a while' it's been. There's no point in asking if he's sure, or if he's serious; Natori knows that he is, and besides-- what exactly is there to say about it? Matoba has been... having sex with a bunch of normal human beings trapped in an ayakashi realm for over a year? So it would seem. It would explain the way he approached Natori, at least.]

...I can confirm that the head of the Matoba clan has not been missing for a year and a half. [Even if the clan were covering it up (they would, obviously.), they would never be able to hide it for that long. Putting aside the fact that he had seen Matoba in person fairly recently, with the whole mess with Ban and Natsume in the pottery village.] Though I have no doubt that Nanase-san and the others could cover for you for quite a while if they needed to.