Features of Heraldic Provinces
The chief herald, which may be a person or a body of persons, can decide rules of the heraldry to be followed within their sovereign's province(s). There may also be some over-riding rules that the sovereign decides that must be followed in all his provinces and there may be other soveeign rules that apply only within one or more provinces.
It is evident from the above that the rules of separate sovereigns and of the provinces within those sovereign's domains are entirely independent. The prime example of this is that two entirely separate families that live in separate sovereignties can have exactly the same arms (perhaps this is why pennants, at least in England, include the flag of their country).
Having said all the above, we may have a resolution to a knotty problem of quarterings. In England there is a rule that no subject may display or claim as a quartering the arms of the sovereign. The members of the royal family appear to use their sovereign's arms but always with a difference mark, which is usually a label with unique emblems for the individual offspring. What then is the rule for quartering the arms of a sovereign of another country? The primary case of this is the arms of the sovereigns of Castile and Leon which were inherited as quarterings through the daughter(s) of Pedro The Cruel, one of whom married Lionel duke of York and which Castile and Leon quarter has been inherited through all heiress descents from Lionel and Isobel.
For some years I wondered whether we could really display that quartering in England. Surely it offended against the rules of English heraldry? Surely we could not claim the sovereign arms of Castile and Leon? Eventually I came to the view that Castile and Leon was not within the English heraldic province nor within any set of countries with a common sovereign, so the rule simply did not apply.
All comments gratefully received.