I think there is no way to proof if you or CJS used the key, there isnt such a log
Neither of us did, However, as you can see in the upper right, user account Jbmeth007, also newest screenshot shows BO2 which was first half of order. I suppose CJS gets their keys from somewhere or someone. There is a log via steam, but that information isn't available outside internal office as far as I am aware. Why, I have no idea?