That fish eater’s website is good. However, I couldn’t help but notice that it says for a British Cardinal, one is to address him as Your Grace. I have never known this to be correct - only that he is to be referred to in the same way one would refer to any Cardinal (Your Eminence).
Similarly, exceptions to the rules regarding Archbishops and Bishops in Commonwealth countries is true, but only when the said person had a diocese there. Titular dioceses do not qualify. It must also be noted that due to the Church of England, the use of such titles (which borrow from the peerage system - e.g. an Archbishop is the equivalent of a Duke) for Catholic Arch/Bishops is not formally recognised.
It can all be very confusing - I was at an ordination to the priesthood recently, where the ordaining Archbishop was english, but was in fact an Apostolic Nuncio, and because his archdiocese was not in England, he was referred to as Your Excellency. Although he did have a titular diocese in Scotland. So I was thrown until I got books out on the subject. Debrett’s New Guide to Etiquette and Modern Manners is an excellent book for this kind of thing.
It also highlights some other really interesting things - like how to close a formal letter to the Pope:
I have the honour to be,
Most Holy Father,
Your Holiness’s humble and obedient child (servant if you’re not a Catholic).