Page 163 of the Shepherd book says this:
"A mystery remains as to the meaning of the letters imprinted below the name Duofold. The letters N, P, Y and Z were stamped there for some reason, possibly to identify the group or company that made the nib and in order to maintain quality control. Unsatisfactory nibs might be returned to an outside manufacturer as rejects."
See, I think Paul was a clever guy who figured nobody would ever figure out he was adding his initial to nib imprints. Everyone would just assume it meant "Parker". Norman spotted what Paul was doing and for awhile the two enjoyed their little inside joke. Yancey and Zachary ruined the whole thing by getting caught right off the bat. The shop foreman, fearing repercussions, kept the whole thing quiet.
Tim