The Swartz Safety previously mentioned in #5 (it requires the grip safety to be squeezed to unblock the firing pin) dates from just before WWII. I think the only GMs made by Colt at that time which incorporated it were .38 Supers, and not very many of those. It didn't affect the trigger mechanism in any way. The plan was to eventually use it in .45 pistols also, but WWII intervened so Colt dropped the idea.