@VICK No one knows for sure what the mintage of the 1955 NSF cent is , because it is a mule and was probably made in error. One theory is that an old useable NSF ( In reality properly called HIGH RELIEF ) die from 1953 was still hanging around and got used for a small run of 1955 cents. In theory this makes sense as there are no PL or Specimen strikes of this coin to the best of my knowledge. This coin vas virtually unheard of until sometimes in the mid 1960's. That is the reason that most are commonly found in fine to very fine condition. There are only 35 graded ICCS mint state examples according to the 2014 ICCS pop report. This compares to the 427 graded pieces in various circulated grades listed in the 2014 report. As you can see the coin is therefore fairly scarce but not impossible to find.
Sincerely hope this helps expand your knowledge on the 1955 NSF cents. Have a good day !