Michael, something else you can see.
The nickel silver disc is shouldered into the copper ring.
The shoulder opens inward in the backplate
The shoulder opens outward on the face plate, so the working thrust is always pressing the nickel silver disc into the shoulder (of course I'm sure it's a tight fit).
The spring, btw, is brazed to a the mounting block, which makes it easy to remove, though I did have to loosen the pawl screw to give me some free play on the pawl (seemed staked at the end, so I didn't push it).