The bag in the listing above is authentic. In this case, the seller describes it as "NWOT" or "new without tags." It may or may not actually be new. (I don't know the seller and I don't know the history of that bag.) (I thought I'd already authenticated it!)
The bag may very well be new however many sellers have been known to describe used or lightly used bags as new. If they think they can get away with it and it doesn't appear to have been used, many sellers think a new bag will garner them a higher sale price.
OTOH, there are legitimate cases of NOS (new old stock) where the bag might be unused but not a current style.
1. Impulse buyers and/or compulsive shoppers might buy something thinking they'll use it and finally, after years of it sitting in a closet, decide to sell it
2. Coach's liberal return policy allows customers to return unused items anytime, without an expiration date. So an older style might show up at a Coach store as a return and be sent to the outlet
3. Coach might do periodic inventory cleanouts and find older items in their warehouses and either send them to the outlets or to discounters.
So the age of the bag and whether it's new or not is not a determining factor re authenticity.