Others, however, see that the switch between the identities of Lilith and Adam are more of a retcon that was made to repair a mistake in the earlier episodes. They think that the writers either confused the two creatures with one another from the very start, while others entertain the idea that Lilith was simply made up on the spot sometime after Episode 15 to include Humans more intimately into the Angelic battle for Instrumentality. One of the reasons why they think this, is because of Kaworu's reaction to Lilith in Episode 24, particularly the Extended Video Version of Ep 24.
In the original OA of Ep 24, Kaworu seems to believe all the time that Adam is in the basement of Nerv, and who knows about all this weird Lilith stuff? Nobody really just yet. Not the audience, that's for sure. He steals Asuka's dormant Unit 02 to use as a bodyguard against Shinji's synchronized Unit 01, and breaks into Dogma only to find that, OMG! That's not Adam. That's Lilith. This. Changes. EVERYTHING.
However, in the Extended Video release, we have this weird scene placed sometime before Kaworu's cave-diving adventures. In it, Kaworu is told by Seele themselves that Adam is somewhere other than the basement.
So why would Kaowru go into the basement expecting to find Adam anyway? He even seems to still be referring to Lilith as "Adam."
Why would Kaworu go into the basement if he already knew Adam wasn't there? I mean, that's the only reason why Angels go into Nerv's basement, right? To find Adam and merge with him? (Or her? Kaworu did call Adam "Mother.")
"Easy answer," I hear you all saying. "It's a plot hole! Plain and simple." I, however, hesitate to call it such.
Remember back to that confusing conversation in the Extended scene? The one that revealed to Kaworu where Adam really was? There was a bit more to it than that. They also talk of Gendo prematurely "closing Pandora's Box."
Also, the scene in where Kaworu gets some dramatic edge-lighting.
This is the interesting part to me. In this scene they are referring to Lilith, the mother of Lilin, as man's "Hope." The way in which they refer to this speaks more of preventing this from happening, destroying it even, before the Lilim can access Lilith.
This give Kaworu reason to go down into Nerv's basement. He probably knows of the whole plan at this point. (Do you honestly think Seele wouldn't educate their Sleeper Angel Agent before deploying him on a mission?) He doesn't believe in Man's "Hope," ("You're saying that is the Lilim's hope?") and he's going to remove it from their options. He is finding Lilith, and he's going to destroy her.
When he finally reaches Nerv's basement, he's in the middle of an existential crisis. He's not referring to the creature in front of him as "Adam," rather he's merely thinking through his ultimate purpose in life while destroying man's hope. There he is, about to destroy Man's only hope, and to what end?
I guess that little bed-side talk he had with Shinji was more of a bonding moment than I had realized...
But despite his existential crisis triggered by his relationship with Shinji, he still seems to be trying to go through with this plan. So what triggers him to finally turn away from his mission and literally keep man's hope alive?
Lilith speaks to him.
We've seen Lilith speak later on in the series. We didn't hear it, but we've seen it. She speaks to Rei in EoE.
Some translations say "Welcome home," others say "Welcome back."
And in the moments of Lilith speaking to Rei, the framing and blocking matches pretty well with the scene of Kaworu's realization in front of Lilith. This can be seen as the filmmakers trying to visually clue us in onto what's going on my comparing the two images we see in the telling of the story.
Now, we're not shown what it was Lilith said to Kaowru. What she said wan't important. What's important was Kaworu's response to Lilith. He squints his eyes for a few seconds at first, as though reacting to something that only he can hear. And then...
Whatever Lilith might have told him was enough to give Kaworu reason to go with his changed heart and not destroy man's only hope. And, just like every good Angel in the series, he parts way with us through death by the hand of an Evangelion Unit.
What do you guys think? Does this theory hold any water? Or am I just spinning my wheels about this?