Nothing to do with dropping (the one I have suffer this but was never dropped but used) nor handling nor age (the other one was very old but not used and was in perfect condition).
It is just the weakness all(?) N950 displays suffer.
It may be the result from usage or just material flaw.

Maybe someone knows it better?

My black spots are more like dotted liney in the middle. Others had them like this one here. So maybe hard pressure (from resistive N900 users? ).