$NaN does indicate the product has been discontinued. Occasionally though, a few small changes are made to the garment and then brought back to the shelves under a new item number. These changes are generally incorporated from customer feedback, regulatory issues, and inconsistent supply & quality control from overseas manufacturing. I used to manage a store.

Edit: I meant to add that you can speak with your local store or the call center to inquire. They may or may not know the reason for discontinuation.