Canonical defection just got harder to prove
The Notification (para. 2) rejects an understanding of "formal defection" that would accept as proof of formal defection those curious documents that dioceses around the world get from time to time (in my experience, they were all from Germany) whereby the local bishop is duly informed that so-and-so, baptized in his diocese, has renounced before a government official his or her Catholic identity--and thereby gets a religious tax break.
St. Paul, I suspect, will have some rather strict things to say to such folks on Judgment Day, but personally I hesitated to read these documents as anything more than money-saving schemes filled out by lazy and/or badly catechized Catholics. That hunch (and I think it was widely shared) now seems verified by the Pontifical Commission, which clearly views formal defection from the Church as an action much closer in character to apostasy, heresy, or schism, than one comparable to a "fill-out-the-form-and-save-a-few-euros" gimmick. I think that's good.
Some other important issues raised by the Notification are best discussed elsewhere, but perhaps one more quick observation is in order: Because it is now clearly harder to prove that a given Catholic has defected formally from ecclesiastical communion, that means that the number of Catholics still bound by the requirement of canonical form (1983 CIC 1108 and 1117) for marriage is higher than some might have thought, which in turn means that more "marriages outside the Church" can be found null for violating canonical form. My impression is that US tribunals had already adopted a narrow reading of "formal defection" to begin with, so the actual impact of this Notification on raw numbers in US marriage cases will be small, but to the degree the Notification has any effect in this area, it would be to increase, not decrease, the number of annulments.
April 18: Jimmy Akin points out some practical problems associated with this surprising interpertation of the law.
Here's another question: Catholics have a "proper pastor" in their bishop (1983 CIC 369) and in their parish priest (1983 CIC 515 § 1). It is not clear to me, then, how at least two distinct men, who obviously need not agree in their reading of the facts in a specific case, are simultaneously "uniquely qualified" to decide whether a given act counts as a "formal defection" (Notif. para. 5). Moreover, the use of the word "Ordinary" in para. 5 still has the feel of "diocesan bishop" about it, despite 1983 CIC 134 underscoring that when canon law means bishop, it will say "bishop".
As I suggested above, there are several other questions occasioned by this Notification, and time will doubtless help us sort them out. In the meantime, here's one for the dogmaticians: Is the phrase "Semel baptizatus, semper baptizatus" (which the Notif. para. 7 clearly and correctly upholds) identical in meaning to "Semel Catholicus, semper Catholicus"?; and another for the Church historians: "Would most (indeed, would any?) of the 16th-century Reformers have been considered to have "formally defected" from the Church under this interpretation?
April 27: Further discussion off-blog.