I have been trying to research the Mil-k 818 series of knives (aka the demo tool or Camillus 1760). I am wondering what exactly are the differences between the letter variations? I know the last change was dropping the pin from the screw driver cap lifter blade, so that would be the change from 818C to 818D, but what were the changes between the Mil-k 818 A and mil-k 818 B? Any information would be helpful, thanks!