The Decker didn’t have the priming capability. Addition of the priming punch was one of Huntington’s improvements. He also changed the linkage sometime after his production started to bring the shell holder to a “top dead center” configuration to maximize leverage.
I asked RCBS Customer Service if they still had priming stakes for the Compac Press. The guy said no parts were available any more, and I had to seriously jog his memory before he even admitted that RCBS had ever sold such a thing.