In importing of items or customers, it is important to correctly define and map the Column ID and  fields to the CSV column headers. When doing the item update using import, it will check for the Column ID defined  and use that to determine what needs to be update.  If the column ID didn’t match, it will not update the items.

Please read this article to learn and follow how items are imported thru the import feature.

http://help.imsunny.com/how-to-import-items/