The Pens By Popularity list is unfortunately imprecise because different people spell the same pen’s brand and model differently (a feature, not a bug, by the way). To investigate this effect, I manually merged all the Franklin-Christoph Model 46 pen counts. As of today, it first appears at #164, with a count of 54. There are 10 different spellings of this brand+model; summing their counts gives a total of 156 pens.
As a second example, their Model p66 first appears at #204 with a count of 45. Summing the counts under 11 different spellings gives a total of 104 pens.
I’ve given it some thought, and don’t see a realistic way to address this imprecision. The Pens By Popularity list is at most a curiosity, not useful statistically. And for brands that are prone to multiple spellings, it is actually deceiving.
I am not suggesting any changes to Fountain Pen’s Companion, beyond at most a little warning text. People have fun looking at the list, and I bet it was easy to generate. Wheras automatic or forced merging is impractical.
You are right, that is a pretty poor list. In the end what I would need to do, is implement something for the pens like I do for the inks. Some day I will, but it’s quite a lot of work and I haven’t had the time nor the desire to do so.
This blog post explains all the work that goes into maintaining the ink list: https://www.fountainpencompanion.com/blog/1-behind-the-scenes-at-fpc-headquarters