[Ron Ramirez]

There's your answer - some "collector" took a pocket knife and widened the hole just enough to make the older (1933-34) Model 16 escutcheon fit.

There are even two sets of screw holes visible - obviously one set for the proper escutcheon, and one set for the older, incorrect one.

Had this been done at the factory, the hole would have been hexagonal as were the original holes for the older Model 16 escutcheons.