Arya's ability checks whether or not she has one or more duplicate(s). This is binary - you either have a duplicate or you don't have any duplicates. Provided she has one or more, she gains one Military icon.
Some abilities put cards into play facedown. A facedown card has no inherent attributes other than “facedown card,” but it may be granted attributes by the card ability that put it into play. A player may look at the identity of any facedown card that is in play and under his or her control.