This pen was originally labeled as a prototype when I found the cap lying in a parts box at the Columbus Pen Show 2000. But a full FP was subsequently found by my friend Lee Chait at the Chicago Pen Show 2001.
What is curious about this pattern is that it has 30 lines going around the cap and barrel. After discussing this mystery pattern with Eric Fonville, a fellow Parker 75 collector, it became quite clear that this pattern has the same longitudinal lines and spacing as that found on the Insignia pattern.
Notice how the lines from the mystery pattern can be simply extended onto the Insignia barrel and line up perfectly. Furthermore, the shallow depth of these lines are similar. The inference from these observations is that Parker used the same tool to make the mystery pattern as they did when making the Insignia. It is just that this mystery pattern omitted the step that put the circular lines onto the cap and barrel as was done to the Insignia.