There is Godzilla 1954-84. Those all are in the same universe. Then 1985 to 1999 minus the USA one is another continuality. Then the ones ending in Final Wars ignore everything besides themselves, 1954 and dimes 98.
What is interesting is that Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack
makes a fun reference to the 98 American movie poking some fun at it.