So why would the states Catalytic converter database show 2 required?
Maybe the person entering the information thought that DBC/Dual Bed Cat meant 2 cats?
I wonder if they did think it was 2 different cats. Back in the day, within a dual bed cat you would have the reduction bed/puck up front, and the oxidation bed/puck in the rear. Some of those cats had an inlet between them for air to be injected into the oxidation bed. Introducing oxygen before the reduction bed would cancel out reduction process. Nowadays, there are no DBCs, everything is TWC.
Anyway, as I said, I dunno.
Why make it simple, when it will work equally as well complicated.