I have had a couple of vintage pens with a divot/ding somewhere on the cap at the same level as the clips ball tip.
I have done a lot of ding and scratch repairs but this is one I never really put a lot of thought to on how they happened. Then I was thinking about how rigid some of the clips are and I, myself have heard the click of the ball hitting the cap when pulling a pen from my shirt pocket. I am assuming this repeated removal from the pocket over a number of years is most likely what causes this particular ding on vintage caps?