Sometimes things don't fit perfectly, because what would be the plot was not 100% done, there were most ideas to be modeled.
So, let's try to think about points in the series that seem like a changed from first concepts or acts that would alow the creators to manipulate the plot with more freedom and plot twists that changed what we were thinking
I'll start listing some:
>Nomura made "young Xehanort" look like Terra a little, so that new Xehanort forms apearence wouldn't have to be always Terra related.
>Nobodies' original human appearence. I guess that by CoM and KH2, it was commom sense that nobodies wouldn't look 100% like their original humans. Roxas appearence reminds Sora, Naminé's Kairi and Xemnas to "Tehanort" painting.
Later we saw that only special nobodies didn't look exactly the human form, Roxas hair was even changed in texture in FM+ to look more like Vens' hair if I am not mistaken.
>People look alike and it's just coincidence: Ventus and Sora.
So, similar to what the guy on the topic below said, "nomura hadnt planned any of this from the beginning".
http://kh13.com/forum/topic/33576-possible-spoilers-ansem-facial-structure/
Sometimes things don't fit perfectly, because what would be the plot was not 100% done, there were most ideas to be modeled.
So, let's try to think about points in the series that seem like a changed from first concepts or acts that would alow the creators to manipulate the plot with more freedom and plot twists that changed what we were thinking
I'll start listing some:
>Nomura made "young Xehanort" look like Terra a little, so that new Xehanort forms apearence wouldn't have to be always Terra related.
>Nobodies' original human appearence. I guess that by CoM and KH2, it was commom sense that nobodies wouldn't look 100% like their original humans. Roxas appearence reminds Sora, Naminé's Kairi and Xemnas to "Tehanort" painting.
Later we saw that only special nobodies didn't look exactly the human form, Roxas hair was even changed in texture in FM+ to look more like Vens' hair if I am not mistaken.
>People look alike and it's just coincidence: Ventus and Sora.
>Time travel: the ultimate plot hole maker.