Books in print really doesn't mean much beyond the publisher's belief in the potential of a book. A large print run says something about their expectations. It is really difficult to determine sales because the books are in so many different places: the warehouse, sitting in bookstores, on people's shelves. Once a month my publisher tells me my numbers but all they have are books in and out of the warehouse. (And the number of ebooks sold). Bookscan tracks "point of purchase sales" - which are actual customers buying actual books - but they don't track all selling sites so they claim they capture 75% of the sales but in comparing my bookscan numbers to my publisher's numbers mine are about 65%. Royalty statements don't help because of "return reserve" When I got my first royalty statement I was disappointed because my sales didn't look very good but then I learned only 35% of the sales were on the royalty statement as 65% were being held in the "reserve." I know get 'unit ledgers" with my royalty reports so I see how many came in and out of the warehouse, but how many will be returned in the future? Very hard to say. The other thing to keep in mind is that format plays a big factor in numbers. Someone in mass market paperback is expected (and if hitting this list does) sell a lot more copies then someone put out in trade paperback where even though their numbers are much smaller would still be considered a success by the publisher.