So, on bookscan vs royalty statements, it's a little bit complicated, so bear with me.
Thing #1: Royalty statements are based upon copies shipped. Bookscan is based upon copies SOLD TO CONSUMERS, and doesn't generally include ebook sales. Therefore, over the life of a book, bookscan CANNOT be higher than royalty statements, or there's a serious error somewhere. You can't sell more copies than your publisher shipped. (Because again, bookscan only covers physical books. this does not include target or costco either...)
However, you have to take into account that there may be a singular statement or two where you have higher bookscan than royalty statements. Because of the timing.
Say your book comes out January 1. Your royalty statement is for January 1 to June 30. Your publisher ships 20,000 copies. Therefore, your royalty statements say you sold 20,000 copies.Did you actually SELL those? No. Your publisher sold them to bookstores. They are returnable.
By contrast, for those 26 weeks during the first royalty period, you sold 250 copies to READERS every week. Your bookscan numbers show 6,500 copies sold. (YES, that means bookscan says 6500, royalty statement says 20,000.) So that means at the end of the royalty period, in bookstores across the country, there are still 13,500 books just sitting around on shelves, waiting to be bought.
Now, let's fast forward to your second royalty statement, July 1 to December 31. Say you are STILL selling 250 copies every single week, and move another 6500 copies. Some stores re-order to fill their stock. But maybe your books don't sell well on the west coast and they ship them back. It's actually possible to end up with net RETURNS (as in negative sales)on a royalty statement even when bookscan shows you sold 6500.Or maybe only 1,000 copies get returned, and 2,000 get purchased. Now you've sold 1,000 copies in a royalty period where bookscan says you've sold 6,500.
But step back. Your overall statements say you've sold 21,000 copies, and bookscan says you've sold 13,000. So your overall royalty statements are still higher. And remember, there's still a whole lot of books sitting in bookstores, waiting to be bought. Your publisher already credited you those sales, but bookscan won't pick them up until Suzy Reader walks up to the register and purchases the book.
That's why it's complicated. Your publisher could over print or over ship in the first statement and show really slow sales on the second one, but meanwhile consumers are still buying it.
That said-- if your bookcan is higher than your cumulative royalty statements, then you have a problem.