When your file has 18,067 books and your inventory shows 18,108, you no longer have to ask us why. After every inventory upload, the results page, the results email and the Files tab of Upload Inventory explain the count step by step: the rows read from your file, rows set aside (a SKU repeated, or a row with neither SKU nor title), items kept that were not in the file (sold items in a catalog, items you entered by hand), and the total.

See the items lists exactly which items were kept. On the Files tab, the calculator icon beside an upload opens the same breakdown days later. The Files tab also tells you which upload of a file was actually processed, even when the same file name arrives every week.