Well the collective observations of Bruno and Dick have pointed out the glaringly obvious, which I was completely oblivious to like usual. Imagine my surprise to look inside and see a perfect little round head of a rivet staring back at me. Wot? #-o
I was blinded by the two holes on the exterior, and presumed they were nail holes, and I was wrong. They were for rivets to hold the front visor rim on. On the exterior they have broken off leaving holes, but that one little remaining rivet head inside removes any doubt. Duh.
Here is a close up of that amazing M1824 Adler in Neusilber.