I think the new/unused is getting a little pedantic, provided a precise definition is included in the description it would have to be a rather stupid buyer complaining about an unused vintage postcard being 100 years old if it was listed as new.
If I complete a painting and not list it for a few months does that make it secondhand or unused or is it still new, what about the age of the subject if I paint a historical scene. Some common sense is required here.