"The movie wasn't really derived from Dark Shadows - they developed a whole new script for that particular one"

This quote by David Selby suggests that the film adaptation of Dark Shadows was not based upon the original source product. Rather, the filmmakers developed an entirely brand-new script for the motion picture. This implies that the film was not a direct adaptation of the initial series, however rather a reimagining of the story. It is likely that the filmmakers wanted to produce a special experience for viewers, instead of merely retelling the very same story. This could be seen as a method of honoring the original source product, while also creating something new and interesting. By creating a new script, the filmmakers had the ability to check out new ideas and styles, while still remaining true to the initial story. This quote shows that the filmmakers were committed to developing an unique experience for audiences, instead of merely reworking the exact same story.