You have seen the movies where it says the following is based on a true story. I use to be impressed with that expecting that the movie would be upfront and accurate from the story they took it from . That came tumbling down with the first of the Jason Bourne movies. Walking out of the movie theater I asked my husband, who had read the book, how accurate was it. He said, “ My name is Jason Bourne.” He then proceeded to walk to our vehicle. Catching up I inquired more of how it was accurate. He said that is it. I think I remember that line correctly.
How true do you want your book to be? How much do you want it to be accurate to a story or headline you are writing it from? As writers or movie makers we can take a wide leap and a huge circle of license to complete the story line.
Now when I hear this statement I take it with a grain of salt. When a movie is based on a book if it is decent enough I will go back to the book and read to see how much they used versus how much they changed the outcome.
It does come down to the artist and how they want to proceed with the project. But it be nice if they write that it is based on a true story that a portion of it is accurate and not just the statement alone.
Sharon C. Williams-Author 
Great post, Sharon. I may have a little something to add here. Since I started adapting my own novel into a screenplay series, getting professional notes, and understanding the process of casting, I have learned that a lot of liberties are taken when writing book-to-film projects. Everything is about pace, character, story, and action. The hardest thing for me was cutting out a lot of dialogue because it was dragging the scenes on for too long. For every written page in a script counts for 1 minute of onscreen time, so scenes are kept usually to about 1 to 3 pages long, with some going as long as 5 or more, depending on the reputation of the writer and director. This important factor is why most films based on books do not always follow closely to the original material. And everything has to be written as SHOW not TELL, which is totally opposite writing novels.
We have a few screenwriters in one of my writing groups. It’s very hard for us to critique or edit it because we weren’t used to that format or how to do it. We’re learning slowly the differences and similarities between the two. I do see what you have brought up. Excellent points my friend. 🙂