Bob, if you are referring to the hing cap. I can't be 100% sure but my guess is that the slot is so one can accses and install the hing bolt, then the tab cover is screwed to cover the hinge. So being I am not actually using the hinge blocks like I am and did on the prototype and Angie these are just scale details. Using the carbon fiber replicated the hing pretty good. One could also put a HD hing here and then in the finishing cover it with the tabe.
TB