True, if you look at it that way, then the later games are the contradictory ones but still, that doesn't mean they can't edit small details just so that the story as a whole is more consistent.
Not only that but the newer games have made the story the way it is now. Kingdom Hearts wasn't meant to be a series in the first place so yeah.
I knew KH wasn't meant to be a series, and which led to the many problems it has today depending on who you are.
Still though if you're making a game or movie that is to be a sequel or even a prequel you always keep the original in mind no matter the series. So if there is contradictory stuff in the first game of a series once a sequel is made it's only because they didn't stay true to it, and that's on them(developers).
Still though when you edit some things it can take away from the first game or even later games experiences that's a risk you run when remaking a movie or game.