You are correct. The only things which limitthe number of pistols you can carry on a CPL in WA state are finances, imagination, and strength. Many of us open carry folk will carry a BUG concealed at ALL times we are OCing, (thus requiring a CPL, but not because of the OC-carried handgun). I routinely carry two guns when I can get away with it.
There was an OC get-together a while back where there was a contest as to how many guns one person could carry. I won, with 5. Funny thing was, I was CCing them all when I stopped by Safeway on the way to the gathering.