Well, I can answer the nut and bolt, that was me, from memory the original bamboo peg split when I knocked it out, from memory it was quite dark on the ends, but this was approx 15 years ago. What made me look closer is I own a couple of cheaper modern katanas, whilst both razor sharp like this particular sword, when playing around cutting some yellow tongue (plastic joiner used in flooring, also great for running wires) the cheaper ones chipped, cheapest close to the tsuba, better one nearer the kissaki, the older one, barely a mark closer the kissaki. It's definitely not alloy, and while I'm no scientist, I've been working with metals for over 20 years, and this was definitely not something made in my lifetime.
Either way, have found it very interesting, who knows, could of just been someone's home project.
Have attached pics of damage to cheaper blades for reference.