The Super 500G on top, and the two Elite on bottom. These two Elite have different filling systems. The most modern shows a CON-50 converter.
Later on have I discovered a missing –for me, that is—link between those two pens. This is the Pilot Elite equipped with a bellows filler. Externally, this pen is very similar, if not identical, to the cartridge-converter Elite. My unit of the later is dated on October 1972 and uses the current gamut of Pilot cartridges and converters save the CON-70 due to the size of the barrel.
The three nibs. The faceted one for the Super 500G, and the more common and well known of the Elite pens. Only one of them, belonging to the cartridge/converter unit is dated: October 1972.
Now, was there another missing link? A Pilot Elite with double spare cartridges could indeed have existed. If so, it might be a quite rare pen given the short life of those cartridges, soon replaced by those we find on most current Pilot models.
Again, a mere speculation, but the search continues.