Model Number Starts with N

N just means it is a replacement. It doesn’t say whether it is new or refurbished. If you send it back they will just send you another phone with an N, or maybe an F (Refurbished). The service agreement says that a replacement can be either new or refurbished. But, as the 11 is discontinued, there are no more new iPhones of that model.

That means it's a service replacement. If were to purchase one, it wouldn't really be a consideration because an older device vs one that might have been factory refurbished more recently doesn't matter to me. An older, but completely original iPhone could be in worse shape than a recently refurbished device.

Apple doesn't consider any of that when they accept devices for trade-in. All they care about is the condition.