I have a 1940's vintage Field Grade FW 12 Gauge. It has the safety lever with the little round hole at the front. When it's "on-safe", an "S" is visible thru this hole. It's my understanding that any LC Smith with this type of safety has the 3 position feature. However, on my gun, the safety cannot be moved backward from the on-safe position. Is my understanding wrong or is the safety not working properly?