I have improved 3 tiles, and yet the craftsmanship Eureka has not activated, as seen in the picture. I have an oil mine, a mercury quarry, and a farm. I think what happened was that a flood pillaged the farm tile, which was my first improvement. I improved the mercury last, which I did while the farm was still pillaged. As a result, I had 2 working improvements and 1 pillaged improvement. That probably disqualified me from the eureka, which is understandable. However, when I repaired that farm, I still didn't get the eureka, which is definitely a bug. Sorry, this is probably not a new bug, but it was the first time I've seen it.