Your comment sparked my curiosity. Java Random[0] which is used for terraine generation uses only 48 out of the 64 bits of the seed, so there are 2^16 seeds for each possible world.[1]

Apparently only the land/ocean biome generation stage utilises the full seed.

[0] https://docs.oracle.com/javase/7/docs/api/java/util/Random.h...

[1] https://www.minecraftforum.net/forums/minecraft-java-edition...