Q Online Sales Report By Category

There is no explanation in the wiki about this particular report.  I'm looking for a little more information as to how it works.  Does it look at what products are in a particular category and then pulls up the data of how many times a product was purchased within the date range specified?  The reason I am asking is that I don't think I am getting accurate data (it seems I am missing data) and am curious if there is some sort of connection between the report and the category that the product was in when the customer added the product to their shopping cart.  For example, if a product exists in two categories and was only purchased once on a particular day, would that report only site the sale if you choose the category it was purchased from?