I would have to dig out my books to see for sure when changes occurred but Belgian marks changed over the years as regards to choke. At some point in time chokes were marked by giving a bore size plus choke size. At other points in time the barrels were simply marked "Choke" if they had at least .2mm (.008") of restriction. what you are likely encountering on these barrels is they were marked at provisional proof & then polished some prior to final proof at which time they were re-marked with the slightly larger size, has nothing to do with the chokes.
