Whether we like it or not, the ownership of land permits the owner unlimited control of use of the land unless it violates local or other land use regulations. Period. I had a cache placed on land with permission of the owner and the property was sold. The new owner was from "away" and closed all uses to her property and in spite of my efforts to educate her about caching, she didn't want anybody on this very rural property on the Choate Road in Windsor.
But there may be an issue here with TNC and that is what is called "slander of title." If they claim my property is their property without basis, then they have "slandered" my good title to my land and they can be sued. If the facts clearly show that the TNC is claiming title to land they clearly don't know, I would notify the lawful owner and tell them so they can stop the TNC in their tracks.
That said, we cache placers have an obligation to not engage landowners unless we are CERTAIN our cache is properly placed with permission of the real landowner. It's like deer hunters who take the "we hunted here for years" attitude. It's not good for the game so make sure of the facts if you want to challenge somebody's ownership.
Sometimes the road less traveled is less traveled for a reason.