Four Gods series and Pilot BB

Hi,
I saw that you had uploaded this image, noticed its title, and my ignorance compelled me to ask you the following question about it:

If the pens form a series called/inspired by the 'Four Gods', why are there five pens?

 

Will you perhaps be adding this picture (and the explanation that I seek) to your superb 'Dating Pelikan fountain pen' thread?

 

Slàinte,
M.