So I was able to use an archaeologist in my last game. He had 4 items that was able to procure and then vanished. For the rest of the game, I was unable to build another (it didn't matter in the end, I still won my Culture Victory). I am guessing it was because I did not have any more slots for anything else of that type. There were still plenty of sites I could dig and I wanted to, but how many buildings can even hold those items? I was Scotland and sadly, the British Museum is only for England.