Here's an interesting fact that I just learned by looking at version exclusives. The pokemon that did not appear in Pokemon Yellow were:
Beedrill <An oddball? Arbok Raichu Persian Weezing Jynx Electabuzz Magmar
Is this further support for them being a trio? Another interesting note is that the Jynx trade was removed in the Japanese Blue version and was relocated to the Seafoam islands.
The Seafoam islands also had Articuno and the Power Plant that featured Electabuzz also had Zapdos. However the Pokemon Mansion which had Magmar did not have Moltres. The mansion is described in-game as being burned down however this is accredited to Mewtwo.
The mansion that was located on Cinnabar Island featured a fire type gym leader. This island was situated on an active volcano as seen in HGSS. In the FRLG remakes Moltres was relocated from Victory Road to the dormant volcano that is Mt. Ember.
Was this perhaps to pay respect to the creator's original idea? Perhaps Moltres was initially intended to be within the mansion but the idea was later scrapped. Or perhaps Jynx, Electabuzz and Magmar were actually the original legendary trio?
How exactly did beedrill not exist? Or do you mean those whole lines?
Sorry if I confused you. That was my fault entirely. I mean version exclusives as in what they player can obtain in-game as opposed to the other version's exclusives. And yes, aside from pikachu I listed evolutionary lines.