I entered two seeds (original and shadow) that they are supposed to have same biome layouts. Here are the seeds and screenshots of these happenings.
Seed 1 - original
Seed -7379792620528906220 - shadow seed but different biome layouts
Expected result: Both original and shadow seeds are supposed to have same biome layouts.
Observed result: Both original and shadow seeds have different biome layouts.
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Comments 3
slicedlime's video is not an official source, but he stated that now the world uses all 64 bits of the seed when avaliable to generate the world, so that every seed is unique ("there's no longer any common factor between different seeds depending on which bits they have in common"), which to me is a very positive change. But this was not cited directly in the changelogs.
This can be intended as a side effect of making seeds more unique.