If it's in a library, it's going to be in special collections, and nobody's going to see it. It will be preserved and kept safe for the rare scholar who has a legitimate need to see the original, but for most purposes the archetype is never needed. We don't have the archetype of Vergil's Aeneid, but it's well studied nonetheless.

If it's in a private collection, a scholar who really, really needs to see it might make an arrangement with the owner. For everyone else, though, there are copies at the local bookstore. Bonus, though: if it's in a private collection, there's a chance that it physically is in a library. Some private collections are housed inside public (usually university) library special collections. From the investor's standpoint, it's worth it to have professionals who know preservation keeping the book in climate-controlled, reasonably secure facilities.