I noticed that you mentioned a duvet - is it feather down? Cats, and dogs for that matter, are notorious for peeing on feather down comforters. I have to get rid of mine because of one bad cat. He never peed on anything else that he wasn't supposed to - just that. When I took it in to the cleaners - they said it was very common - I figure they are the experts in that realm.
Love Them & Lead Them,
~Elizabeth & Doug
Dog Training the Way Nature Intended