Tielby
Prince
Another possibility has to do with the density of existing features. If you're using the Blessing of Armathaon, especially on a smaller map, this becomes a problem. As I recall, there's a table somewhere of which resources are placed in what order, and if no valid sites (they can't be too close to each other, like cities) remain, the ones at the bottom are simply not placed. I only remember this because it used to be a problem with reagents being toward the bottom of the list, meaning that most civs couldn't get mages. I don't know how, or even if, this problem was resolved, but nobody's complained about it in a while.
Just throwing out possibilities.
Just throwing out possibilities.