As a variety hunter...I say the challenge on a 52 D would be finding one that isnt a rpm. 25 listed varieties for the date & mm.
I do not think it is a RPM, as if you have a large screen the IGWT and Liberty show some similar shapes. If it is just a RPM , there would be no similar effect in that area from a repunch. IMO, Yes, I think die deterioration myself. Sorry Jim
From VV. It also has the matching die crack and die breaks. http://www.varietyvista.com/02a LC RPMs Vol 1/1952DRPM008.htm