Khan;
Old standards were more or less a full choke had 1 mm of constriction. The other chokes were a fraction of that. Subtracting your choke diameters from bore diameter gives .55mm Right & .75mm Left. That would be essentially 1/2 & 3/4 chokes or what we usually refer to in America as Modified & Improved Modified. With modern shells it may well pattern tighter than that.
The 18.35 also indicates the bore is a bit undersize @ .7244", not at all uncommon nor anything to be concerned about. This does point out though why it is necessary to know the bore size to determine intended choke for measuring the choke. Choke is not a Size, but an amount of constriction. A "Nominal" 12 gauge diameter of .729" = 18.52mm
