Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
A Tale Intended to be After the Fact. Being the Experience of Four Men Sunk from the Steamer Commodore
Okay, this isn't exactly an epigraph; it's really like a subtitle, in characteristically nineteenth-century fashion. (For real, have you ever spent any time with old eighteenth- and nineteenth-century texts? Their titles are so ridiculously long and boring.)
If any of the Harry Potter books had been released in 1845, their full titles would have been something like Harry Potter and the Philosopher's Stone: A Tale of a Young English Boy Whose Doesn't Realize He Comes from a Magical Family; including His Arrival at His Wizarding School; and His Discovering His True Heritage; and His Brave Battles Against the Forces of Evil.
Anway, we do think this subtitle deserves mention, as it makes clear that this story is a tale, after the fact. This is what we today call "Based on a True Story." Take note of it.