True: a backtest is a wager on the recorded past, and it is only as good as the record. A decade ago the story everywhere was big data, big data, big data. This is where I am supposed to say AI changed everything. The unglamorous half is compliance: everything a data provider hands a trading desk answers to the policies of dozens of exchanges and other information providers, and the good data companies get very good at managing those requirements. But the data’s got to be good.