Why the changes?

Wonder why they change some of the story lines from what actually happened. Is there some kind of block on using certain people's stories?
The story line on how The Family met Patricia/Katie Krenwinkle is not right. To the best of my knowledge, she was working in insurance and not a grocery store. And she met Manson at a friend of her sister's apartment. She was one of his first followers.
And also the story with the guy he served time with and food poisoned is fake too. Thinking they are gonna have him as the drug dealer Manson shot right before the murders.
I understand they add more to the story to make it interesting for TV. But I just wonder if they can't really go into certain people's parts in the real story because of legality or something.