You are right (not the part about example 1) -- the corner will pop out going forward, not to the side.
As for the button, as long as the part that slides in and locks is still good, it will hold the corner in. Just pop it in, and check to see if the corner is loose. The diamond thing you're talking about, I have a broken one on one side too, but it still holds very securely.
Also, in case you go to the dealer asking... I don't know what that button thing is called, but it's not a self tapping screw (it's not even a screw). A self tapping screw usually refers to a sheetmetal screw that is pointy, as opposed to a screw with a flat bottom. It means that you can take the screw and drive it in without having to tap a hole first. Just FYI
Good luck man.