Anaphora of Addai and Mari + Anglican Orders

I was reading the other day about the anniversary of a Vatican document recognizing the validity of this ancient Christian eucharistic prayer. As many may know, this prayer used by the "Nestorian" Assyrian Church of the East does not have an "Institution Narrative" (with the words, "This is my Body"- "This is the chalice of my Blood"). For this reason, it has been considered invalid in the past by Roman Catholic theologians, and the Chaldeans who came into communion with the Pope of Rome had to insert these words into their liturgy. The reversal of this opinion by the Holy See has been called the greatest doctrinal decision since Vatican II and the Council of Trent.

While I was reading this document, I could not help but reflect on how this would affect the argument of those who still say that Anglican orders are invalid. The former position of the Roman Catholic Church, that the words of Institution are the words of consecration and thus absolutely necessary to confect the sacrament, was very clearly defined dogmatically, and it was supposed, once and for all during the Middle Ages. This is a total about-face, and one that I do not necessarily disagree with.

If this de fide position was wrong, what are we to say about Leo XIII decision that Anglican orders are absolutely invalid? It was not a de fide decision, and the basis for why he decided in that manner is much less strong than why Latin theologians thought this ancient anaphora was invalid. The Roman objection, as I understand it, states that the grade of order is not mentioned in the ordination prayer, and that the intent is not the same as handing down the priesthood or episcopacy as the ancient Church understood it. On the latter, I think that this has changed in the Roman Church as well since the time of Leo XIII; the prayers of ordination are not the same. On the former, we can say if the Vatican could change its mind on the necessity of the words of institution in a Eucharistic prayer, it cannot be certain of the invalidity of Anglican ordination when the Prayer Book is very clear what order is being passed on in the ordination service.

You can't have your cake and eat it too. Either Roman Catholic sacramental theology is consistent, or it is uncertain.