I think I can answer most of it, but maybe I'm confused between the terms: Baptism of Desire AND Baptism by implicit desireMike, actually, the only dogmatic place that this issue is taught is at the Council of Trent, in three places. The first place is in session 6, chapter 4. There it states:
"Chapter 4. A Description of the Justification of the Sinner, and Its Mode in the State of Grace is Recommended: "In these words a description of the justification of a sinner is given as being a translation from that state in which man is born a child of the first Adam to the state of grace and of the adoption of the sons' of God through the second Adam, Jesus Christ, our Savior; and this translation after the promulgation of the Gospel cannot be erected except through the laver of regeneration, or a desire for it, as it is written: Unless a man be born again of water and the Holy Spirit, he cannot enter into the kingdom of God.'"Here, the Latin word for "desire" is "votum," which is normally translated as "vow" or "promise," as it is, for example, preponderantly throughout the Douay-Rheims bible. It can also mean "desire," but a desire to fulfill a vow or promise. In addition, the Latin reads as "vow of baptism" (or "desire of baptism"), rather than "baptism of desire." Hence, the use of "baptism of desire" is actually a inadvertent juxtaposition of the Latin words, and unfortunately, often gives the connotation that "desire" itself is a substitute for baptism. The Latin, however, speaks more specifically to the individual's prior knowledge of baptism, and thus his "desire" to fulfill his promise to receive baptism, rather than a "baptism of desire."
This distinction can be seen in one of the other times that Trent uses the idea of "desire." In session 6, chapter 14, it reads:
"Hence it must be taught that the repentance of a Christian after his fall is very different from that at his baptism, and that it includes not only a cessation from sins, and a detestation of them, or a contrite and humble heart' [Psalm 50:19], but also the sacramental confession of the same, at least in desire, and to be made in its season, and sacerdotal absolution, as well as satisfaction by fasting, almsgiving, prayers, and other devout exercises of the spiritual life, not indeed for the eternal punishment, which is remitted together with the guilt either by the sacrament or the desire of the sacrament, but for the temporal punishment [Canon 30], which (as the Sacred Writings teach) is not always wholly remitted, as is done in baptism..."Here the individual is understood as one who already knows of his responsibility to receive absolution in Confession for his sin, but perchance, doesn't live long enough to do so. In that case, the "desire" to fulfill his promise to go to Confession is sufficient. His "vow" to do so is reinforced by the other committments he must honor, e.g., "as well as satisfaction by fasting, almsgiving, prayers, and other devout exercises of the spiritual life."
The 1992 Catechism also teaches the same. In paragraph 1258 it states:
"The Church has always held the firm conviction that those who suffer death for the sake of the faith without having received Baptism are baptized by their death for and with Christ. This Baptism of blood, like the desire for Baptism, brings about the fruits of Baptism without being a sacrament."Notice that the Catechism does not call it "the baptism of desire," but "the desire for Baptism," which distinction acknowledges that the person fulfilling the category is one who already knows of his responsibility to receive baptism.
This is confirmed by the next paragraph of the Catechism (1259) which reiterates the Traditional interpretation of Trent's chapter 4 on the "desire for baptism," that is, that the "desire for baptism" applies in the first sense to catechumens. It states:
"For catechumens who die before their Baptism, their explicit desire to receive it, together with repentance for their sins, and charity, assures them the salvation that they were not able to receive through the sacrament."The last time "desire" is mentioned at Trent is in Canon 4 on the Sacraments:
"Canon 4: If anyone shall say that the sacraments of the New Law are not necessary for salvation, but are superfluous, and that, although all are not necessary for every individual, without them or without the desire of them through faith alone men obtain from God the grace of justification: let him be anathema."Again, we see that Trent, as did the Catechism, stresses the "desire for" the sacraments, not the "sacraments of desire." It is clearly stated that one who does not receive baptism or confession has not received the sacrament, even though they "desired" the sacrament. In other words, the "desire" for the sacrament does not mean they have received the sacrament. They will be saved without the sacrament (but only if they had a desire for the sacrament).
Theology is all about making the proper distinctions, and this is one of those times that proper distinctions must be made.
All that I have said above is what has traditionally been taught of Baptism and the desire for it, and is reiterated in the 1992 Catechism.
The speculative and non-resolved implications of "desire for baptism" concern the issue of those who may have sought God in their lives, but had no knowledge of their responsibility to be baptised, or even knew of baptism. What is to be done for these kinds of people? The Church has not given a definitive answer on this question, just as she has not given a definitive answer on the eternal destiny of an infant who dies without baptism. These issues are covered in paragraphs 1260 and 1261 of the Catechism, but you will see by the language that the author is non-committal in his answer, that is, he does not claim to be giving a dogmatic answer to either question, but only gives "suppositions." In the end, as Pius XI taught, our knowledge concerning the recipients of salvation will take us only so far and no further, and to speculate beyond that point is not our prerogative.
God be with you.