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DR, what constitutes the minimum that must be believed to have supernatural faith is unknown.  St. Thomas said belief in Christ was necessary, but later theologians say that the belief need only be implicit.  Even St. Thomas said something about implicit faith somewhere.  

Someone who has implicit faith DOES have a belief in Christ, you know.  It's just an implicit belief in Christ.  Just as his membership in the Church is one of desire.

You ask if false understandings of the minimum that must be believed to have supernatural faith have implications for the Magisterium.  If the answer is "yes," the implications are caused not by those who believe in implicit faith, but those who deny it i.e. the Feeneyites.  It is very possible that, since Pius IX, the idea of implicit faith is a dogma ( it's hard to say ).  But the trend over time is definitely towards the idea that belief in a God who is a Rewarder is the minimum that's necessary.

There is an apparent connection in many minds between Vatican II heresy and implicit faith, which almost seems like some kind of "lead-in" to Vatican II.  Father Feeney is thus painted as a kind of Cassandra trying to stop the Greeks from accepting the Trojan horse.  But when I say this is an "apparent" connection, I use the word advisedly, since "apparent" is not the same as "real."

Actually the two concepts -- implicit faith and Vatican II heresy -- are totally distinct.  Implicit faith has been discussed by theologians going back to the Salamanca school and probably before.  You could even say it is "implicit" in the very idea of baptism of desire.  Vatican II heresy also has deep roots, even deeper roots you might say.  These are roots that go right back to Judaization and the mystery of iniquity.  

But they are nevertheless two totally different concepts.  Implicit faith says that someone who is in invincible ignorance may be disposed to believe in Christ, and may thus be a member of the Church by desire, even without knowing it.  Vatican II heresy comes in different forms, for instance, they say or imply that other churches have salvific value in themselves, or are somehow part and parcel of the Catholic Church without knowing it, thus blurring them together, or that the Old Covenant has never been revoked, etc.  This is not the same as implicit faith.  The concept of implicit faith does not say "A Protestant is saved by the Protestant church."  It says "A Protestant may be a Catholic without knowing it, presuming he's never heard of the Catholic Church yet is internally disposed to be a Catholic."

I really don't understand why this bothers some people, or why it used to bother me.  People act as if the idea of implicit faith means there is no point to engage in missionary activity,  like it sucks the purpose out of going to far-flung, dangerous places and baptizing people.  How so?  We don't know if two people or two billion people are saved in this way, by being members of the Church by desire only.  But we do know that it is an extraordinary way that someone can be saved, and certainly not something to count on.  

The point is, God CAN save someone this way if He chooses, but how often does He choose to do it?  This is what we don't know and will never know.  There is no reason to leave people in ignorance thinking they'll be better off, because we do know that to be baptized is much better than not to be baptized, don't we?  Not only do you get the mark on your soul, not only is it a sacrament that makes one an explicit member of the Church, but someone who is baptized has the chance to develop in the faith and is likely to attain a much higher place in heaven than someone who only has implicit faith...

It is better to be baptized, a "duh" statement if there ever was one.  This remains true even if God saves a certain number of others -- a number known only to Himself -- without baptism.  God does what He does, we do what we can do, which is to spread the faith.  If God chooses to save some people in an extraordinary way that doesn't require our intervention, that doesn't mean we should sit on our hands and do nothing, because His will dictates that in other circuмstances, in all likelihood MOST circuмstances, He does require our intervention.

Monsignor Joseph Fenton, American Ecclesiastical Review, February, 1951, pages 124-143:

The idea that a votum, that is a desire or an intention, of entering the Church can bring a man “within” the Church sufficiently to allow for the possibility of his salvation is one of the dominant factors in recent theological writing on the Church’s necessity. The notion itself is a part of Catholic doctrinal tradition, although this particular terminology, or, to be more exact, the application of this terminology to the thesis that there is no salvation outside the Church, goes back only to the latter part of the sixteenth century, to the time of Stapleton and St. Robert. [57] Now the idea, and to a lesser extent the terminology itself, is definitely a standard part of the scholastic treatment of this thesis.

Likewise, and by force of the very content of Catholic theology, it is standard scholastic teaching that the votum or desire of entering the Catholic Church may be merely implicit and still sufficient to bring a man “within” the Church so as to make his salvation possible. Salvific faith must be explicit on four points. No man can believe in God as he must believe in order to possess the life of sanctifying grace without distinctly acknowledging the existence of God as the Head of the supernatural order, the fact that God thus rewards the good and punishes evil, the mystery of the Blessed Trinity, and the mystery of the Incarnation. The mystery of the Catholic Church is not one of these facts which must be believed explicitly in salvific faith.

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