Locks on the left side are of course very common on flint and percussion double barrel guns, with either side-by-side barrels or superposed. But on old, original single barrel guns, I've seen only a couple with left hand locks over many years... to me they sure look strange. More common is an arrangement with the lock on the right side and a cheekpiece on both sides of the stock to better accommodate a "lefty"
With regard to "helpful teachers", for several years in our Philadelphia public school they tried to force my classmate into being right-handed. Not only did they fail, but my buddy developed a terrible stutter. He was denied enlistment into the marines in the late 1950's because of this stutter (It broke his heart as his father was a combat marine in WWII)