Since there's no written history of cocktails, how were you able to discern between the multiple "truths" you were no doubt given by the various historians and bartenders that you interviewed?
There were "Rashomon" moments from time to time, where people remembered recent history differently. That sort of thing will happen when researching any sort of history, and particularly in a history that took place mainly in bars, where memories of the night or the week or year before can get hazy. One of the more amusing instances concerns the invention of the Trinidad Sour, a modern classic cocktail. The stories put forth by bartender Giuseppe Gonzalez, who invented the drink, and Julie Reiner, who employed him at the time, come nowhere near each other. But this sort of thing happened less often than you might think. Where there were conflicting accounts, I relied on the additional recollections of outside sources, people who didn't have a stake in that particular slice of history. When you're drawing on five or six primary sources, it's a safe bet that you'll land somewhere close to the actual truth of what happened.