I've read, from the early 1960's, that the standard 12 bore full choke is 40 "points" of choke, thus a nominal 12 bore, at .730", subtract .040" (thou) is .690", the standard 40 "Points" of choke.
Until some gun makers started over-boring, or 'back' boring to larger than 12 gauge (like .735" to .740") "to reduce recoil", .040" was the standard. Perhaps the standard today is .035" or 35 "points" of choke?

Good post.

Further confusion comes with shot sizing. It can vary, from country to country as to hardness and # per ounce for any given size of shot.

Weighing out an ounce and counting is the only positive way of knowing, to make accurate patterning percentages.