What, you may wonder, happened to the Decree to the Armenians of Eugene IV? Try looking in the index of the CCC; you will not find it. It has been buried. There is a lesson for us here; magisterial documents, even if issued by a Pope with the consent of an Ecumenical Council in a context of making sure that dissidents returning to Full Communion, really do understand the Faith, can quietly evaporate (if you think I'm pulling a fast one there, go and check up how many of the canons of Nicaea are still in situ today).
Eugene IV remained a problem for Latin theologians, not least when historical studies revealed how late the invention of the Porrection of the Instruments was. If it is necessary jure divino, then there are no valid orders anywhere in Christendom. Some theologians resorted to suggesting that the Church, which has the charge of the Sacraments, may have changed the Form and Matter at some time, to make the Porrection into the Matter instead of the ancient Imposition of Hands. The most learned pope of the last half-millennium, Papa Lambertini, aka Benedict XIV, would have none of this theory. He quoted Trent (sessio 21 capitulum 2) against it, and went on "Then, even granted that the Church had the ability to do what we are talking about, it is a completely empty and arbitrary claim that the Church used that ability. Let [those theologians] say where and when, in which century, in which council, by which pontiff, the change of this sort was done. ... But since all the elements, which were contained in the ancient rituals, survive intact, and even now are performed in their holy integrity, nobody will easily believe that those things which formerly were sufficient [i.e. ordination by imposition of hands], nowadays are insufficient to complete the Sacrament of Order".
That was in the middle of the eighteenth century. You may well wonder why the rules requiring the complete reordination of any westerner who missed the Porrection of the Instruments survived more than two hundred years after a learned pontiff, albeit writing as a private theologian, had spoken so frankly.
>>Magisterial documents are not set immutably in stone. Ad Armenios is no more.
>>Benedict XIV, like Benedict XVI, did not believe that popes and councils had unlimited power; he denied they could change the Matter and Form of the Sacraments.
>>But Rome is immensely careful. Since the validity of the Sacraments is so crucially important, it took two centuries - until the whole scholarly establishment had agreed that Benedict XIV was right - before his conclusion became, under Pius XII, the law of the Church. But even then, Pius XII covered all the possibilities by adding "If, at any time by the will and decree of the Church the Porrection of the Instruments has also been necessary for validity, everyone knows that the Church has the power to change and abrogate what she has decreed".
>>How much sounder this care with the things of God is than the cheerful Anglican irresponsibility which introduces doubt into the Sacraments of our Redemption in accordance with the transient fancy or whimsy of a particular period; whether of the mid-sixteenth century or the late twentieth. It is of that irresponsibility that modern Anglican Catholics have to pay the price when their Orders are regarded by some as invalid. Blame, not Pope Leo XIII; not even Cardinal Vaughan; but Cranmer and - in our own time - the General Synod