it is not about the bloodline as such, it is about the living tradition, the story.
Is it not strange that someone like Sanya not just descends from Saladin but knows it and immediately says it when asked?
And I do not think it was ever presented as a necessary condition, just as something that helps.
Or used to help in the past. Maybe Butters broke with more than one tradition.
Im not convinced this is true. Not because I dont think it's necessary for the connection to be Known, but I dont think it is operating on the mechanisms of "Belief", nor does it need to be Known, persay. For one thing, it will always be Known, by the Universal Truth stuff that Ghost-harry tapped into, and also thanks to the Archive. But for another, this is a
Heavenly Power that is (By WOJ) based on the aspect of Responsibility inherent in Royal Lineage. Given how TWG's forces have always professed to work regarding Free Will and chains of Choices, I think it's entirely possible that it needs to be a legitimate (if not necessarily direct/linear) connection of Inheritance from a Mortal that made a Choice (and/or made Oaths) to be Responsible for his/her fellow Mortals. Even if the false tradition of Lineage is centuries old and firmly anchored in history and the minds of the populace, Heaven would still know that the requisite Choice was never made for that line.
The real difference being that a False royal tradition (entirely common historically) would not work, it would have to be legit. It also means that, in theory, a
New Royal line could arise, given the right situation and Responsibility.
Is it not strange that someone like Sanya not just descends from Saladin but knows it and immediately says it when asked?
Not really, but that's only because he's a freaking Knight and the Universe tells them things in strange ways; for all I know the archangel that dropped off Esperacchius just referred to him as "Saladin's heir" through the conversation. Similarly we only know of the Carpenter/Charlemagne connection because of the research done by an apprentice wizard, which may easily have included anything from supernatural sources of information to Council records (kept by a sub-race of super-long-lived scholars that are themselves a bit obsessed with the genealogy of magical talents. And our third Data-point is Shiro, who's genealogy research was also done by wizards, and in general Japan has a much more complete and/longstanding cultural tradition of accurate Genealogy records.
All that to say that our datapoints are all abnormal enough to be suspect.