Not at all. Especially since its an adaptation of a book, meaning you can adapt and play with it until the sun dies out. Every writer can take a stab at their own interpretation of it. Back to the future isn't based on a book, its the sole idea of two guys who were looking around a garage, found a picture and wondered what it'd be like to go to high school with their parents. Our generation will say "oh hey its like that movie I may have loved when I was a kid" but another generation can see it and get some entirely new shyt while it still being true to the source material. The 95 movie takes liberties with the book just like this does, so one adaptation is just as reasonable as the other.
It's no different from there being 3 or 4 versions of the wizard of oz, 2 versions of Charlie and the Chocolate Factory, multiple versions of peter pan, and multiple versions of alice in wonderland. And thats not even including stage plays.