I would think the model designation " Mlo ____" would be stamped or engraved somewhere on the gun- trigger guard tang or water table ? The 12 was one of the highest grades offered by VS - should be totally engraved including barrel wedges. Terry Wieland had picture of an 11E in his book - extensive engraving ( a few too many " pterodactyl(sp?)" ducks IMO - but deeply carved ) see photos in his color plates.
best regards,
JBP