In Europe, perhaps, but I worked at a Los Angeles area Peugeot/Nishiki dealership from spring 1972 through summer 1974, and that horrid Simplex stem shift system arrived late in my tenure.

Those two rivet holes on the BB are indeed where the original serial number plate was mounted. There is no way to know whether the number stamped into the dropout matched this number or was arbitrarily chosen by a bike shop, a police station, or even a prevoius owner.