The .809 & .806 certainly sound like the chamber, though this will be a taper. If just ahed of the rim seat would be on small side, but if just behind forcing cone would be on large side. The .700 & .727 indeed sound like muzzle measurements & would seem to indicate the cyl & the choke difference.
Where the 12 & 13 come into play is between these two measurements. Measurements were made at that point in time by a simple plug gauge turned to a specific dia, in the sizes mentioned. The bbl was marked per the largest size plug which would enter the bore, from the breech, to a distance of 9". To compare present size with the "Proof Size" you need a measuring tool which can reach into the bore beyond the chamber & forcing cone.