The myth of The Night of the Night of the Sicilian Vespers would be good topic. For close to 30 years the story of Luciano and his men killing 40 Mustache Petes to take over Mafia was written about and portrayed in many Mafia books and films. Then it was revealed by a historian to have been a hoax.
Another story on Luciano written about in many books and movies was his participation in murder of Joe Masseria. That tale was told over and over, of him taking Joe the Boss to a restaurant to set him up for a shooting and getting up and leaving table so he would not be at table when gunmen came in. That one was shown to be false after someone found the police reports of the slaying. Those are 2 big long time myths that many still might believe.