It is a factor, Turi. One of the biggest problems in trying to do research on gangsters and organized crime is that these fellows seldom write dusty books of memoirs, or leave their collected papers to universities, to be perused by the likes of you or me. In fact, most of them were illiterate, and those who could write, didn't, for fear of breaking omerta, or otherwise divulging grist for prosecutors. So, contemporary journalistic accounts are just about the only sources that authors can rely on. That said, Asbury's book is pretty much the only semi-authoritative source on that period of time in NYC's history. And at least some of what he wrote has been verified by other authors.