The first couple of Heisei films were ambiguous, the third assumed it was the original, but the concluding film of the series explicitly indicated that it was a second, distinct Godzilla. (My best rationalization is that they originally believed it to be the original but later figured out it was a separate one.)
That or the temporal shenanigans from Godzilla vs. King Ghidorah
had something to do with it.
Yeah, but that's exactly the film that creates the problem. It assumes there was only one Godzilla who survived the original film, that his mutation was a unique event. That's why they go back in time and try to prevent it. Yet several years later, G vs. Destoroyah
explicitly says that the Oxygen Destroyer killed the first Godzilla.
Of course, the temporal logic in GvKG is totally incoherent. Even though they go back in time and alter history so that Godzilla has disappeared when they return to the present (only to re-emerge in a more powerful form soon thereafter), everyone remembers that he was there just before the time travel.
Which is not the way changing history works. But that's where my theory allows reconciling that mess of a movie, if you squint a little. We can pretend that what they're actually remembering is the 1954 attack by the original Godzilla, who was killed. And the time travel would've then undone the events of The Return of Godzilla
and Godzilla vs. Biollante
as well as the first act of GvKG, since it was actually the second Godzilla whose origin they altered; they just didn't realize at the time that there had been more than one.
Except that doesn't work either, because in Godzilla vs. SpaceGodzilla
, Biollante's battle with Godzilla is remembered. Then again, GvSG is a totally horrible, stupid movie, and Destoroyah
pretty much ignores it anyway, so it's easy enough to dismiss it as never having happened. And then the Heisei chronology can almost, approximately make sense.