I have done this a couple of times. I just register the watch on the Patek website. I have never received any correspondence back about the watch already being registered nor have I been asked to prove that I am in posession of the watch I'm registering . It kind of makes me wonder if anyone at Patek really looks at these registrations. I like to think that they can punch up any watch they've made and have a provenance for it, or that they can pull up my name and see a list of watches that I own. Is this wishful thinking??
Steve