I have a early G 12 with 30 inch Damascus tubes, a project gun. I have shot it at clays and pigeons with BP and lo-pressure 2.5" RST hulls- nice old economy grade gun, DT, extractors. I went to the LeFever site, mine is SN 24xxx made about 1894-95, has the sears on the sideplates and the single cocking hook design. I found out that after about SN 25xxx LeFever re-designed the mechanism and put the sears inside the stock, but as this IeFever I presently own is the only one I have dis-assembled (removed the sideplates only) I can't say for certain.
Mine has a "less bulky" appearance at the breech, has the take up screw with the two spanner wrench holes, weighs about 7 lbs. 6 oz. and balances at the hinge pin. Nice gun, but NOT a Parker by a long shot. DU had an article a few years ago by Ron Spomer on doubles, believe they had a 16 gauge Optomist Grade shown, very fine looking gun indeed.