"Based on a true story" is a come-on, the aesthetic equivalent of "no loan request refused." For, at best, the creator has fashioned a film based on his understanding of, interpretation of, and reduction of the report of an actual occurrence.
David MametWriting a novel is an incredibly free experience. One puts one's self in a narrative mode. You can go off in any direction - the past, the future, or go laterally, or include one's own beliefs. It's total freedom.
David Mamet