Resources outside city bounds

[Summoner]

I just lost one of my two coal resources to a culture border shift. My second's 3 squares away from my nearest city, but within my cultural borders, has a mine, and has a rail link to it. The game's saying I'm without coal though. I could've sworn I'd used other resources that were 3 away from a city though.

Am I missing something, or just misremembering here?

 

[BTSFanRandy]

Perhaps you could build a fort on it?

 

[Summoner]

I was missing something. I was trading 1 coal to ab AI. *DOH*