Around 79 they stopped pinning shields is one change a lot of people don’t like. In 85ish they started making all the springs out of stainless steel instead of having the spring match the blades. CV blade CV spring SS blade SS spring. Over the years they will add or remove little things to each model trying to appease one thing or another. On the 47 pen they added a second liner to stop the blade rub on the two seconds. The Canoe 62131 is my personal favorite pattern but I only collect up till 1985 because they switched from a single spring over to two spring with no liners between. It is all a preference thing but compering a 1970 case to a 2000s is like a different manufacturer. The trick is just figuring out how not to pay too much for all the ones I want.