The order knows the importance of keeping Pluto around, even if they declassified, because they cannot draw attention to the fact that it’s actually a huge space station that is populated by the highest members of the order. This is something that could create some speculation and Pluto is not to be targeted for humans to conduct studies. The good news is that there is no way for humans to see any of the structures in Pluto because they are all underground and the entrances are hidden perfectly.
There might be a point when Pluto will be revealed for what it is and perhaps they will allow for humans to take credit for it. Otherwise it could be unveiled as an alien structure that was abandoned by the aliens, but the order will never let humans find any important information or materials there.