2-piper, I believe your info is all good but my understanding is that a gun pre-1887 with a 9 or 9B/10M stamp would remain in proof as long as the bore remained between .803 and .835 . The " not for ball" and "choke" stampings would help to confirm the date of proofing either pre or post 1887. Knowing when the gun was proofed is the tricky bit. It was the manufacture of lighter guns and therefore thiner barrel walls that necessitated the fractionalization of the bore sizes.
Terry

Better to keep your mouth shut and be thought stupid,than open it and confirm.