The New York Times Bestseller List: while you might think you know what it means, you may not be sure how books get on it, or why they don't, or why one book is on a different list than another. This post will attempt to explain these things.
Here we go:
1. There are three lists that a YA book can land on. One is the children's chapter books list. These include chapter books for younger readers (ages 7-10), middle grade, and young adult. The second is the children's paperback list-- the same, except for paperback releases. The third is the children's series list. I'm not clear on the rules about when a series is considered a series on this particular list. It seems to be the third book in a continuous series (like The Hunger Games), but not a third book in a series of companion novels (like Graceling, Fire, and Bitterblue). In any case, once a series is considered a series by the New York Times list people, its individual books can't be on the other two lists, even if they have higher sales.
2. It's on a week delay. You may have noticed that if you see authors, editors, agents, or other industry professionals posting/tweeting/etc. about a book that just got on the bestseller list, and then check the New York Times Best-Sellers website, the book is not there. That's because publishers find out which books are on the list a week before the list is published, and publishers will usually then contact authors and agents with that information. If you check back in a week, you'll see the book in question.
3. Just because a book isn't on the list, doesn't mean it's not doing really well. In order for a book to get on the list, it has to sell a large quantity in a given week. Consider these two fictitious books: Book A gets a big push for its release, sells a lot that first week, hits the list, and falls off the next week. Book B doesn't get a big push, sells consistently well for several weeks, and never hits the list. Book A and Book B could sell the same number of copies cumulatively! But because Book B never got that big swell, it never made the list.
4. A book can get on the list, come off the list, and get back on again. There is no fixed number of copies a book has to sell in order to make it on the list. All it has to do is sell more relative to other books. So if a book has been on the list consistently for several weeks, then gets knocked off by another book's release, it can still pop back on the list again if it keeps selling. It just depends on how the other books do.
5. Pre-orders don't necessarily count toward the list. This is because pre-orders are handled like regular sales: they are counted when they ship, which is when the credit card is charged. If books are shipped early, as most pre-orders are, they won't count toward release week sales.
6. E-books don't count either (on the children's lists). I don't know what else to say about this, other than: that could be a huge portion of a book's sales!
7. Some places/sites that sell books don't report their sales. As far as I know, Amazon and various wholesalers do not report their sales. This means that those figures are not accounted for when a book gets on the list, and their absence may account for a book not getting on it. I'm sure it's possible for Book 1 to sell more copies, all told, than Book 2, in a given week, yet Book 1 doesn't get on the list when Book 2 does, though I don't have a specific example to give.
8. It's not the end-all, be-all of bestseller lists, though it is the most famous. There's also an Indie list, a USA Today list, an Amazon list, and a bunch of others that are difficult to crack but express a different (or more complete, depending on the list) portion of sales. A book can also be an international bestseller, meaning it's kicking butt and taking names in non-US markets.
So, to summarize. What the New York Times bestseller list ISN'T: perfectly indicative of a book's success, or The Only Thing That Counts.
What the New York Times bestseller list IS: a reflection of a book doing very well in a particular week and suggestive of healthy sales, as well as a really, really exciting thing for all those involved.