Questions regarding four speed hump.

So I got the original four speed hump out of my 1970 Dart and was wondering what the welded on tab was for? (the thing at the top of the pic) My only guess would be a stopper for the bench seat so it doesn't hit the boot?

This is the AMD piece and I was wondering why the bottom screw hole is missing and has a notch in that area instead? Don't I need the lower screw hole for the chrome trim ring? (I don't have a trim ring to see)