I have read several threads regarding artifacts that say there is only one copy of each artifact in a given game, and in general, that comports with my experience. However, last night, I managed to obtain two of the same artifact. I completed the second leg of the Olivia Ross quest where you build an expedition at her last known location, and you receive the Ross Weed artifact once you complete the expedition. Previously, I had received the Ross Weed artifact from pillaging an alien nest, so I now have two copies in inventory. (Sorry, no screen shot at present, but I can provide it if anyone has doubts.) It seems like there is a Supremacy quest that also gives an Old Earth artifact - some kind of mind-operated helmet - over the course of the quest. I can only assume the same scenario would be possible there. Not sure if the devs meant for this to happen or not, but I just thought I'd point out this little curiosity to add to the body of knowledge on artifacts.