This page is just my own personal opinion on the two unknown patterns on the previous page. Mind you, I have no proof supporting this but I believe it is correct.
I think those two unknown patterns were definitely not Parker factory-issued pens; instead I believe them to be after-market products having been worked on by non-Parker artisans. This idea is not as alien as you might think as Parker has had a history of working with prestige marques such as Boucheron, allowing fantastic and valuable pieces to be created. What else would you call a jewel-encrusted writing instrument?
However, the two in question are far from the quality of a Parker, and definitely not a Boucheron. Just take a close look at the poor quality and inconsistency of the engraving of the lines to create the patterns, especially those in the first unknown pattern. My guess is that this was not done by anyone in France; they're too proud of their workmanship to let loose something this unrefined.
As to the question of how these pens were made, I have heard speculation about starting out with a lacquer 75 and stripping it of the lacquer. That's certainly possible, but I think I have a simpler answer -- Parker sold blank, brass 75s before they were lacquered. Here is the example I found.
I did not polish it and 10+ years of oxidation certainly takes its toll. It is pretty much the way I found it when I bought it from a French pen dealer. When I inquired what it was called, he simply said he called it "laiton". That's the French word for brass.
In the hands of an unsophisticated engraver, this very pen could be transformed with the floral and vine patterns that you saw on the previous page. And resorting to silver- or gold-plating would certainly hide most of the poor engraving quality and result in the unknown patterns depicted.