Despite the risk of getting sucked into a lengthy discussion.... (as if
anything else were possible with NGE):

The current theory I subscribe to is this...

EVA 01 houses Yui's soul
EVA 02 houses Asuka's mother's soul (who subsequently we crazy and then
commited suicide).
EVA 03 did not house a soul (which would explain how the Angel was able to
infiltrate it)
EVA 04 did not house one either (that went kablooey)
EVA 05-13 are full production models and never had souls tested with them

That said, it has been postulated on more than once (though with very little
evidence) that EVA 00 may have housed Dr. Akagi's soul (Ritsuko's mother).
The only actual evidence is circumstantial (EVA 00's rebellion with Rei
during the sync tests and the assumption that EVA 00 is trying to get to
Gendo).

Like I said -- just a theory...

ChaozEngine