A very belated thank you!
Now something unrelated: in a recent game, something pretty weird and confusing happened to me. That is, I got access to iron at a time when, as far as I could tell, I shouldn't have had access to it yet. One of my cities was working an iron mine and was connected to it by a road, but the city shouldn't really have been trading with my capital yet. It had neither a road connection nor any kind of river or coast connection that I had already explored.
Let me illustrate it with a series of screenshots:
As you can see, I was already working on a road from Birka to Nidaros, but it was far from done yet, and I hadn't yet explored enough of the coastline for a water route. Now, both Birka and the rest of my empire were already connected to the Americans, but I didn't have an Open Borders Agreement with them yet, so that shouldn't have mattered. So what was going on?
Edit: the difficulty was Noble and the mod was BUFFY 3.19.005, if that helps.