Any presumption is just that. It doesn't mean that it can't be set aside. It doesn't even necessarily need to be set aside by an argument from the other side. We could review something that we presume is reliable, but if we look at it and think, “I don't quite understand that, and that's problematic”, we go back to the foreign state and ask them for input.
It's a very give-and-take process. Saying that there's a presumption of reliability is a starting point, but it's not the end point by any means.