FWIW my old '72 PX10 had a deluxe B17 and I'm reasonably certain it was original. Perhaps Brooks Pros were in short supply that year and they filled in with B17 and Ideale saddles as needed.

I'm not sure what they called that model B17 then. It was a bit like the current B17 Imperial, but without a center slot. The lacing holes were bigger in the middle and got smaller at the fore and aft, making a sort of decoration. At the time I didn't know what the holes were for, and assumed it was meant to be drillium or just for looks.