I don't know really. I have a theory that says the bulk of them are genuine, with some mischievous loon muddying the waters a couple of hundred years later. There's one field that looks as if it just rained stones one day! I'm writing a short blog about my experience there that'll probably just add to the confusion. I wonder why the powers that be don't just excavate some of them. Surely there'd be some carbon-dating evidence.