As I posted elsewhere Casso is in a North Dakota (or was it Nebraska? One of those, I can dig it up) maximum security state pen.

I think of the BOP.gov locator as being quite reliable but I am used to navigating it's various quirks. It's rather user friendly compared to some locators.

Another example of this situation (last I checked anyway) is Buford Furrow. If you wanted to write either one you could use the RRM address and they will get the mail. Which is a bit strange for the BOP as they are horrible about forwarding mail but in this case I guess it's on them for giving it as their location.