ykk is simply the brand of the zipper. It does not prove it is authentic. Not saying that it isn't thougjh. YKK is a high end zipper and commonly used by Coach.
Carrine even when the YKK zipper is not a Coach sole item. The YKK zipper is a high end quality zipper used by Coach and posting a picture of the YKK detail will definitely increase the bids on your item...replicas do not use YKK zippers. It's a nice bag! F&W!