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LOL, I wasn't aware there was a Piotrus Principle... thanks for pointing it out ) Yes, occasionally good stuff will be added to non-article pages and needs to be moved to talk. Perhaps an even more fitting name would be 'Reference Desk principle' - I have seen this done often, with impressive explanations on RDH (often by Clio) being turned into articles.
As for DoP issue, I lost track a little - I am not sure which argument of mine do you refer to. But yes, Dukes of Pless should have a separate article from Duchy of Pless at some point; even if most of such articles start as as little but lists of office holders, they have a potential to develop into something more.| talk  "