Although I recognized where he is weak, and had omissions. He tried in the 1940s to gather information from publishers and from trade publications. As a book collector I know that he under-represented some categories. But I always question which books survive on bookstore shelves and in what condition. Many initially weak sellers, in good condition, can stick around bookstores and hence seem more common than they really were.
Sermons are classic examples of that.
Subscription books are a tough area to crack open a sense of accuracy. Demand in the past and in the present both play a role. I used to be a dealer in rare photograph records. The valuable stuff was valuable because of rarity and current collector taste. Learning that lesson I do try to hold onto some popular works since they really do tell us more about the period in question rather than contemporary taste.