As has been explained many times (and pace fact-patterns very rarely encountered) divorced-and-remarried Catholics living as if they were married should not approach for holy Communion per Canon 916 and, if they do approach, ministers should not give them the Sacrament per Canon 915. Therefore, if the pope, immediately (in Amoris) or mediately (by endorsing the Buenos Aires directives), wished to authorize persons living in irregular unions to approach for holy Communion and/or to direct ministers of holy Communion to give the Sacrament to such persons, he would have had to modify or cancel the pontifically-authorized canons unquestionably prohibiting such actions found in his Code of Canon Law.
But canon law is barely a blip in Amoris and neither it, nor the Argentine directives, nor the pope’s endorsement letter so much as mentions Canons 915 or 916, meaning that these two canon laws remain in full force and must be understood and applied as the canonical and moral tradition has long understood and applied them. That, or Francis is the first pope in history to widely and expressly authorize what he plainly and comprehensively prohibits. Which I don’t think is the case.
But now, suppose under some result-driven, eisgetical reading of Amoris and/or the Buenos Aires document, someone argues that Canons 915 and 916 have been derogated from in the case of divorced-and-remarried Catholics, in other words, that Amoris or (even more fantastically) the endlessly malleable verbiage of the Buenos Aires document has the character of universally applicable canon law. What then? Enter Canon 8 § 1 of the 1983 Code of Canon Law which states: “Universal ecclesiastical laws are promulgated by publication in the official commentary Acta Apostolicae Sedis, unless some other manner of promulgation has been prescribed in particular cases.” For over a century the Acta Apostolicae Sedis (Documents of the Apostolic See), a monthly journal subscribed to by few outside of arch/diocesan chanceries and ecclesiastical academe, has been the nearly-exclusive vehicle for publishing the official, binding documents of the Holy See. In just the last several years it has, Deo gratias, been posted on-line (warning: there are many maddening errors in the electronic texts not present in the printed versions). But the Acta Apostolicae Sedis is not a synonym for “Vatican Website” and, however useful that website might be to researchers, it has not been designated as the vehicle for promulgating canon law or equivalent provisions. As it is, moreover, self-evident that no “other manner of publication” was prescribed in Amoris or the pope’s follow-up letter, the appearance of these materials on the Vatican’s website means canonically nothing.
There are, to be sure, many important publications coming out of the Holy See and/or the Vatican City State (L’Osservatore Romano, Communicationes, Enchiridion Vaticanum, the Insegnamenti of recent popes, and so on) some of which carry canonically and magisterially significant documents in a complex (and sometimes confusing) variety of formats. Sorting out these fontes essendi and fontes cognoscendi is stuff for professionals; our focus today is on key points of codified canon law, on some very important disciplinary provisions presented in that law, and specifically on where such laws and norms for pastoral activity are set out authoritatively.