They stampped the blade on one side with the year, ordnance bomb and the company of manufacture. The other side is marked US and the serial number. Early blades were bright but after a point they were parkerized. In the beginning only Springfield and Rock Island Armory made them, but for the second war another nine or so started producing. In 1942 they made long blades but after the feedback came from the troops the blades were either cut short or manufactured short. All of this info is given in detail in books by Canfield or Duff or Brophy to name a few, but that's the nutshell. I still would like a look when you get around to it.