This ‘leather’ costume is a great example of the very common practice in the film and television industry of having multiples of various garments made for a production. Costume duplicates can be produced for a variety of reasons, including copies for stunt doubles, or versions to be used if a garment has to undergo aging, water damage, rips and tears, etc. Having an additional costume on hand ensures that if scenes have to be re-shot, or when scenes filmed out of order (this is almost always the case), that the costume maintains continuity throughout the scenes.
This costume made its first appearance in Joss Whedon’s Buffy the Vampire Slayer, where it was worn on Alyson Hannigan as Willow in the 1999 episode Dopplegangland. Her body double, Jennifer Nicole, can be seen wearing a duplicate of the costume in a behind the scenes photo. There is also a sketch of the costume in the book Buffy the Vampire Slayer: The Watchers Guide, Volume 2 by Nancy Holder.
The outfit was used again on actress Lindsey Stoddart as Katie Ney in 2006 in an episode of Bones entitled The Man with the Bone, though it is not known if the costume that was utilized was the one worn by Alyson Hannigan or by Jennifer Nicole.