There are "historically significant" artifacts which are things that are both original and something about them was also historically important or interesting. And of course artifacts that are historically insignificant but original and so sometimes good examples of items from the time. The Steamboat Arabia museum has a lot of stuff you would find in the 1850's version of WalMart, none of it is historically significant but the items are great examples of what the stuff people were talking about when they wrote letters and books probably looked and felt like.
The key is separating the item (which can be an original, a re-creation[1], a restored original, or a replica) and the context (the item's history)
[1] I believe, but am not sure, that this was the term for something made with the original materials but using different techniques. Some things like Samurai swords have a gap where it was lost how they were made, and so all you get are recreations of swords of that type rather than new original swords. And yes, I know, its all semantics really, but archivists are nothing if not sticklers about details.