Ages ago you asked whether princes in England were automatically Duke of York, etc. And I don't know if you even want to know any more, but I recently discovered that the positions are designed to give the princes income independent of the crown, back when princes went to war and needed to outfit crusades and things. Back when the crown (and duchies) made money off of wool, timber, rents/tenant farmers, and etc. Not sure if this is helpful, but I thought the economic derivation of the position might be something you could use.