If the duct tape came from something else (was removed from one place and then applied to JonBenét's mouth), I would think forensic specialists would be able to determine that - what it had been stuck to (tell-tale fibers for example).

Since the duct tape has been sourced to a run date of November 1996 and probably only hit the retail shelves a very short time before the murder, I doubt this piece of tape was on something else in the house or that it was on the back of a doll that never existed in the Ramsey home - where DID this American doll thing come from? JB got a My Twinn Doll - and it too was shipped before this duct tape manufacturing run was done.