I had this round for years, but the case was split in two places and the penetrator rusty so I decided to do a cutaway and remove the splits and clean it up. After a lot of hand sawing with a jewelers saw I finished and went to put it in the drawer. Only then did I realize that the aluminum base was entirely different than my complete AP-T round. The cutaway round has no headstamp and is plain aluminum. The complete round has an ink stamped headstamp of: AAI 73 25mm AP-T LOT 1-1 and the case is aluminum with a dark gray finish. Was the case finish part of the identification between the two rounds or was this changes in the development of the different rounds?