I just expected a little more information around their data source other than "It's hard to find good data, this proprietary source (so you can't look at it) is

I just expected a little more information around their data source other than "It's hard to find good data, this proprietary source (so you can't look at it) is the best we could find, it has some known biases, but we eyeballed it and it looks good enough". In particular I was looking for a full study that explained what "very similar" meant since the fairness of that input data seems it's key to their results.