Columns from the new spreadsheet will be used to overwrite the current sheet, aside from description and upc, which are ignored. This is because the description from the new sheet has probably not been cleaned as well as your current sheet, right? Also, we do not touch UPC values, since the new sheet will import case UPCs as individual UPCs. We are really focusing on pricing.
Be sure to run this after checking for new skus and caseqty issues. As a test, you can run the new sku check again, and it should give you no results.
If you do get results and can not figure out why, check to see if the results you receive are hidden in your vendor products. That would explain why they are not being matched.
Large file uploads will take a while to process, depending on your internet connection and server load. You can set specific columns to use for matching. The default columns are listed below. Change to suit your needs.