Thanks James. I hadn't noticed the abrasion on the right-hand cartridge which is more central. Cartridge left or right could be candidates for being the last round in the clip - proving that the unspent round was dropped in from the top.
It would be impossible for both of them to be the last one in the clip. Also, those abrasions do not appear to be what I would expect (location and shape and severity) if made from contact with the elevator. So, I think another possibility should be explored.
Another possibility, that seems more likely to me, is that during transportation from New Orleans to the Paine’s garage, the clip might not have been inside the magazine of the rifle. This would be one of the basic safety precautions that most of us are taught regarding firearms. And since the sides of the clip are open, if something relatively hard was up against the clip (say packed tightly inside one of the duffle bags) it and the vibrations of the trip, etc. could make the type of abrasions that we see on two of the cartridges. The very top one would be protected by the top portion of the clip and therefore would not get the same abrasions.