I think the devices have just been flattened and look thicker. I agree with Furry...need to even establish if there are any known DDOs for the date and which variety you think it might be.
VV has two listings for 1951 S but I cannot tell due to the condition from the pics. http://varietyvista.com/01a LC Doubled Dies Vol 1/DDO 1951-S.htm
Looks like something is going on w/ the MM. Almost looks inverted to me..... @furryfrog02 That said.......I can find no info on an inverted mint mark for that year. @Collecting Nut