Re. choke marking on the Merkel 201 E. They may not be marked but if they are they will be marked on the face of the ejector. Earlier guns that I have owned & handled were not marked but I have a 7/92 proofed 203 E that is marked. I'm not exactly sure when they started marking them. The choke will be specified in the certificate provided with the gun(like you show for the 447S)as well as pattern % with a specified shot charge weight & shot size. Choke will be expressed as a fraction ie. 1/1 (full) 1/2 (half) 1/4) (quarter)
except for (improved cylinder) which is marked vz.

BTW, as I'm sure you know the 447S is marked 1/2 & 1/1 on the bbl flats. Full & half choke.

Failing either of the above take it to someone who has a bore micrometer & measure the bore & choke. Bore dia.- choke dia. = constriction. Roughly .040" constriction = full, .020" = half, .010 = quarter, & < .010 = vz or IC.