>>5405690I'm pretty sure that's intentional, though. the 55/62 transition was definitely intended to show it continued from Godzilla Raids again. The early Showa era actually has some pretty tight continuity.
I have a pseudo head canon that the Futurians in vs. King Ghidorah caused the Showa/Heisei timeline split. In the "original" timeline", The second Godzilla showed up a year after the first. The dinosaur that saved Mr. Shindo's platoon wasn't the Godzilla from '54, but the second one. But when the Futurians warped Godzilla's body into the Bering Strait, it was left inert(dead, or just slowly healing) until the 70's when the Russian sub sinks and exposes it to radiation, resurrecting it as the second Godzilla, who now first appears in '84 rather than '55.
Granted, it doesn't explain the absence of Showa King ghidorah, Rodan, or others, but perhaps the Futurians messing with the timeline set things off.