The whole idea of having improvements being able to upgrade and have workers able to build them is foreign to BtS, so it is not supported at all. Hence the problem. I suspect the fix would be coded in the dreaded Main Interface python. Basically we need to do for improvements what is done for routes and not show ones that are downgrades of the one on the plot. edit on the heroic II promotion. The code looks fine but I will move the test for a golden age up front rather than last.