I'm curious about exactly how 00 got her soul in the first place...Shogoki and Nigoki both explicitly had a 'Contact Experiment' with a willing, living subject interacting directly with an Eva, at least, if Yui's Dive Suit is anything to go by...
Yet the main candidates for Zerogoki's resident were both deceased before any 'contact' had taken place...
Can a contact experiment be performed on a corpse? Perhaps it can, but the soul is 'damaged' somehow, and is the cause of Zerogoki's rebellious nature.
Perhaps a soul will flee to a new container if one is nearby...or perhaps it is a unique trait of the souls of the Progenitors of Life...
Specific mention is made in the CI that Seele somehow 'retrieved' Adam's soul, which had fled her body...how did they retrieve it? What form was it in? Was it in an original Kaworu, and the Tabris just a clone of him?
Stupid soul, why do metaphysics never come with an instruction manual? Bah, it'd probably come in Swahili anyway.
On a side note,
According to Sadamoto , its the thoughts akin to between a mother and her child, or two lovers, which fuel synchronisation
Meaning its entirely plausible that the soul of anyone will do, so long as they have some degree of love for the pilot.
Consider then that, if it is Rei1's soul in Zerogoki, then her ability to synchronize is determined by her ability to love herself, specifically, to love who she has become, compared to who she was.
This ties in well to one of the themes of Evangelion, of the individual being able to accept who they are and what they have become.
Addendum: According to the Red Cross Book, Rei was cloned specifically from what was left of Yui's body after the Contact Experiment...which gives a approximate frame of reference for just when Rei1 and Naoko died,
"Don't you touch a hair on that boy's head! Have you no respect? He's mine! Get your own human play-thing, you quartz-brained little creampuff!"
- Bernard Black
"Kaji was the most heartbroken and shattered over Kaji's death besides Misato." -AuraTwilight
Self-admitted meme-whore.Unashamed troper.
O-sensei's House of a Thousand Hearts: Lest We Forget