Hello,
If they actually did “formally defect,” then yes, they would have had no obligation to observe canonical form and the marriage would be valid on that account. However, as “1ke” stated, “formal defection” was defined in such a way that the act of joining another Church (such as the OP describes in his own life) would not have met the requirements of that restrictive definition. If you are interested, the Pontifical Council for Legislative Texts issued this explanation in 2006 and it can be found here:
vatican.va/roman_curia/pontifical_councils/intrptxt/documents/rc_pc_intrptxt_doc_20060313_actus-formalis_en.html
Dan
And the actual dates that formal defection would apply to marriage was from the promulgation of the 1983 CIC till three months after the change was published in A.A.S. So that range is:
November 27, 1983 - December 21, 2010 (inclusive)
And there is a little elaboration here, revised March 2007:
ARCHDIOCESE OF INDIANAPOLIS INVESTIGATION GUIDES FOR FREEDOM TO MARRY IN CASES OF LACK OF CANONICAL FORM
INSTRUCTIONS
2. Significance of Item #5: Did the Catholic leave the Church?
Canon 1117 of the 1983 Code of Canon Law indicates that the Canonical form is to be observed as long as one or the other of the parties has been baptized in the Catholic Church or received into it and has not defected from the Church by formal act. This law limits somewhat the applicability of the Canonical Form of marriage. However, it only affects those marriages which have taken place on or after November 27, 1983. On this date the 1983 Code of Canon Law became effective. Although we have little experience with this law, it would seem to be self-evident that if a Catholic has formally joined another church or has in writing or before witnesses indicated a firm purpose of withdrawal from the Catholic Church, and it is evident that in neither of these situations is the action jocose or obviously ephemeral, then such a person is not bound to the Canonical Form. If such a person after November 27, 1983, entered a marriage with a non-Catholic, a tribunal process would have to be instituted to establish freedom to marry. In doubts about these matters, the form recommends consultation with the Tribunal or the Chancery Office so that assistance can be given in making a judgement about those matters.
- Significance of Item #6: Was this a marriage in an Eastern Orthodox Church?
At the Second Vatican Council, in the decree on the Oriental Churches, the Fathers of the Council declared a new law which enabled Eastern Rite Catholics to contract marriage validly with Eastern Orthodox in the Eastern Orthodox Church, even though such marriages would be illicit without the usual dispensation or permission. In post-Vatican II legislation, the Congregation for the Oriental Church, with the full approval of His Holiness, extended this provision to those cases in which Latin Rite Catholics contract marriage with Eastern Orthodox before the Eastern Orthodox priest. Thus, in those situations, after March 25, 1967, when a Latin Rite Catholic married an Eastern Orthodox person in the Eastern Orthodox Church, such marriages are to be considered valid even though illicit. If you ever seem to have a case like this, it would be well to consult the Tribunal or the Chancery Office.