What are top reasons for incorrect valuation of inventory?

Just saw this question from someone else the other day. I think this is one of those "book things" where it depends on what the author thinks are the "top reasons." It could have been miscounted. I've seen one company count inventory at the sales price instead of at cost. Could just be math errors in calculating it. I don't know what some book considers to be the "top" reasons and I think it would be more useful to try to find this in the text and see what the book has to say. (For instance, they could even divide "math errors" up into several categories and call them different reasons. It's always hard telling how something will be presented in a book.)