>>280591497
In terms of chapters-to-episodes, that sounds about right. The trouble is it's very hard for them to do a proper adaptation without having a strong idea of where the next ~8-10 chapters are going. As we saw with S2, adapting something to a television format requires significant changes in structure and pacing to make it flow (like how KC integrated the Ganja arc so that it was more interspersed through the first two-thirds of the season), and that's almost impossible to do if you don't have the whole (or at least most) of the picture already.
Production of the second season began around mid-2020, just before or just after Vol. 9 dropped. So by that point the Iru arc was basically ~80% done: Everything about the village of the Hollows, Faputa and her motivations, and the tragedy of the Ganja's backstory had been revealed and all that was left was to wrap things up with the last five chapters of the arc, which were nearly all released by the time production of the second season was announced publicly in mid-2021.
I think the earliest KC could have enough of the picture to start on production is about two years, but of course that depends entirely on Tsukushi's output.
