I just finished watching the TV show Fargo. Each episode begins with the lines that this is based on real events. When I looked for it on Wikipedia, it said

However, this claim is completely fictional. Showrunner Noah Hawley continued use of the Coens' device, saying it allowed him to tell “a story in a new way”.

I want to ask, is there no rule/guideline for it? In other words there must be some governing body which checks what contents can be shown and what can not be shown. So is there no rule related to this?