>>2880970>>2880979(cont)
It'll always be unreasonable to infer that Rei's soul was split simply because there exists another theory that Kyoko's was. It does not follow. Because A happens person 1, A did not necessarily happen to person 2. In fact, if I am not mistaken, the idea of "soul divisibility" for Kyoko is not even a proper fact either, but yet another fan theory.
Ritsuko mentions that there's just one Rei Ayanami in episode 23 as well, and no single character, glossary, book or extra bit of canon related to the original series have made the reference to Rei's soul or part of it being inside EVA00. There is however plenty of contextual evidence to infer that what is inside EVA00 is simply prototype dummy plug tech, nothing more.
Particularly the "died hair" theory is reprehensible and a remnant of some idiot's thinking from a long time ago that should be dismissed like the trash it is.