OK, as a paid member I have access to a tool that is supposed to show me Challenges in a given area. As near as I can tell, this map will show challenges that have checkers as green, and those hat do not as yellow. Further, those for which I'm qualified will have a blue do, and those for which I am not will have the red circle with the line through it. See image below.

The labelled cache does indeed have a checker, and appears to indicate I qualify for it. But, since I only have finds in 27 states, that is clearly incorrect. I have noticed a number of other instances in which the map indicates I am qualified for challenges when in fact I am not. What gives?