You hit on a good point about Lansky. As some of us here have often posted, mob figures aren't the types to leave their collected papers to colleges and universities so that people like us can study them. Most of what we get about them comes from newspaper accounts whose accuracy was sketchy to begin with, and often highly sensationalized. The few mob biographies published tend to run with the sensationalized stuff--and even one error gets repeated dozens of times.
In Lansky's case, he was reputed to be "the richest gangster who ever lived...worth $300 million." But Lansky was one of the very few gangsters to have a competent biographer. Robert Lacey, his biographer ("Little Man - Meyer Lansky and the Gangster Life," a wonderful book!) tracked down the $300 million figure to Hank Greenspun, publisher of the Las Vegas Sun, who admitted he heard it second-hand and printed it because it was a big, impressive figure--and it was picked up dozens of times. Lacey said that, at most, Lansky was worth between $5 and $6 million--not chickenfeed, but hardly the stuff of $300 million. The reason that Lansky lived stp 81 and died peacefully, says Lacey, was that "he was the accountant--never the boss." He never acquired the wealth and power that so often lead to jealousy and murder in the Mob.