Haha, I really don't know! I have AC for my MacBook, but never got one for the iPhone (and never had one fail one me since 2009).
My launch Apple Watch actually developed a fault with the screen after 6 weeks, and Apple sent it off. A week later I went to pick it up and it couldn't have been repaired, so they gave me a new one. It came in a square box. I a not sure if it was a new or refurb, but couldn't find anything wrong with it. Am pretty sure it was new, just not in the official retail packaging.
The reason I ask is because I see the watch as much more of a personal item. it is the only gadget that is actually "on" you, so from a personal standpoint, I'd not be keen on a 'refurb'. (Not knocking anyone who does get a 2nd hand/refurb watch).