I think there are probably many more examples like this, but hardly anyone is looking for it now, and while some set ups may be accidental, others certainly aren't. At least some amongst these people were shadow experts. Maen Llia , in particular, is a very clever creation, almost an exhibition piece. A kind of portfolio of megalithic science, all built into one stone and it's setting.
We are not as clever as we sometimes like to think we are.