Late reveals also have some weird effects, since you can build other improvements on that tile first. I had coal appear under a grassland/forest with a lumbermill Building a mine would have given me +1 food, -1 hammer on that tile. Yeah...a mine converts hammers to food. If horses appear on a tile I've already farmed, I'd rather have that than a pasture. Heh...imagine the frustration if every resource appeared with the tech that let you use them. Iron definitely needs an earlier reveal.