There are 2 and 3-stage cats. My guess is that Porsche is doing stage 3 in a separate unit instead of all in one canister. I am not certain of this, however. They could be two 3-way cats in series for all I know.
FWIW, I was also pleased to find out that in CA you no longer have to go with an OEM cat replacement like we used to.
(legislated into law somewhere around 1998 fwd, we had to install high-cost factory OEM units when they went bad )
Now we can buy CARB-approved aftermkt units as we did before 1998. Go figure. Hope somebody here can give you some more clarity to your question.