Read the relevant part of the interview with GAINAX founder and ex-president Toshio Okada here. It occurred in 1996, shortly after the conclusion of Evangelion.
Toshio Okada wrote:I think the style, or mood, of EVANGELION, is not so far, not so different, from the serious side of GUNBUSTER or NADIA. The biggest difference would have been in the style of planning the last episode. My style is to always plan the ending *first,* as I did with GUNBUSTER--everything then follows from that. In NADIA, Mr. Anno couldn't decide on the ending--it wasn't fixed until only three months before the final episode was shown. So subsequently, I was confused about NADIA, and there was a lack of control over the various episodes. EVANGELION is a very great series--I think it's one of the top anime ever made. But--the last scenes were never fixed. When I talked to Mr. Anno a month ago, he said he couldn't decide the ending until the time came. That's his style. So, if I had made EVANGELION with him, I couldn't do such a thing. I'd think I'd have to fix the ending, what would happen with every character. Then, everything would follow: the first episode, the second episode...If I wanted to show a boy's coming-of-age story, a *bildungsroman,* the last scene would show the grown-up man; the first scene, a boy who hates everything about the adult world. That would be the structure; I'm very careful about a regular construction. But Mr. Anno's style on EVANGELION was not so. He wants to put it together episode-by-episode. It's just like the style of a manga. In your typical manga, the artist doesn't have any picture of the last scene, or the last episode. They just think of building up on past episodes. And finally, the manga artist, and his assistants, and editor...[BURIES HEAD IN HANDS], they work out an idea about the last sequence. If it's a good idea, the whole episode is very good. If they can't make a good idea, the whole episode is not so good. It's an unhappy story. And I think that's what happened with the last two episodes of EVANGELION. Mr. Anno and his staff couldn't make a good idea for it. He told an anime magazine in Japan that he couldn't make what he wanted because of schedule or budget. But that's not correct. I talked with Mr. Yamaga and Mr. Anno. They said, "It's not only a problem of schedule or budget. It's a problem of what the ending is going to be." Mr. Anno couldn't decide. Mr. Anno's and my own style of production are very different.
Hey, notice something odd about what Okada says?
Okada wrote:I talked with Mr. Yamaga and Mr. Anno. They said, "It's not only a problem of schedule or budget. It's a problem of what the ending is going to be."
From this interview, we are presented with two facts: Yamaga was well aware that the ending hadn't been decided, despite what he said at Fanime. And keep reading the page to see that Anno gave contradictory answers every time he was asked about the ending. So I wouldn't put it past Yamaga to make crap up. Anno did.
Okada says many other wonderful things about Evangelion, Gunbuster, Wings of Honneamise, and The Simpsons in this interview, so I made a general thread about it here. Use that thread for the other stuff. I'm not sure really how to split it since a lot of the information is on Evangelion and a lot isn't.
Among other important Evangelion-related information is that there were scheduling problems, but they weren't GAINAX's fault, because the animation wasn't done at GAINAX, because GAINAX only had three staff members dedicated to anime. Anno blames the production company Tatsunoko for the scheduling problems.