Bugs me too. If anybody in the West has de jure claims on anything, the Pope has a de jure claim on Rome. Hard to see how the Patrimonium being all de jure Papacy even in 867, or Latium at minimum, wouldn’t be preferable to what we now have. Aren’t there other game mechanics available that result in characters never or infrequently pressing their claims? Hell, if the count of Ancona loves the Pope, why shouldn’t he swear fealty? And anyway, even if there’s a reason it’s unsuitable in 867 is no reason to lock down later start dates.