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Karl Rahner:

But, let us say, a Buddhist monk (or anyone else I might suppose) who, because he follows his conscience, attains salvation and lives in the grace of God; of him I must say that he is an αnσnymσus Christian; if not, I would have to presuppose that there is a genuine path to salvation that really attains that goal, but that simply has nothing to do with Jesus Christ. But I cannot do that. And so if I hold if everyone depends upon Jesus Christ for salvation, and if at the same time I hold that many live in the world who have not expressly recognized Jesus Christ, then there remains in my opinion nothing else but to take up this postulate of an αnσnymσus Christianity.

Archbishop Lefebvre:

God knows all men and He knows that amongst Protestants, Muslims, Buddhists and in the whole of humanity there are men of good will. They receive the grace of baptism without knowing it, but in an effective way. In this way they become part of the Church.

The error consists in thinking that they are saved by their religion.  They are saved in their religion but not by it.

+Lefebvre even claims that these infidels become "PART" of the Church.  That is a very grave error.  What then separate his ecclesiology from that of Vatican II, both of whom believe in a Frankenchurch which includes not only Catholics but even heretics and infidels.

And this part here is downright scandalous:

Many times in Africa I heard one of our catechumens say to me, “Father, baptize me straightaway because if I die before you come again, I shall go to hell.” I told him “No, if you have no mortal sin on your conscience and if you desire baptism, then you already have the grace in you.”

So this man ardently desired Baptism, and +Lefebvre basically told him he didn't need it ... which could serve no other purpose than to, ironically, weaken and undermine his ardent desire for Baptism ... an irony famously pointed out by Fr. Feeney, that BoDers turn people's desire for Baptism into a desire for the desire of Baptism.

So the appropriate response would be either to train some people who remained there how to perform Baptism in the case of an emergency, reassure the souls that if he continued to ardently desire the Sacrament, God would not deny it to him (ask and you shall receive).  Frankly, I would have immєdιαtely baptized the man, declaring "I have not found faith as strong as this in most of the Catholic Church."  In fact, this man had more faith than most Catholics, and, sadly, even more than Archbishop Lefebvre himself on this particular point at least.

So the appropriate response would be either to train some people who remained there how to perform Baptism in the case of an emergency, reassure the souls that if he continued to ardently desire the Sacrament, God would not deny it to him (ask and you shall receive).  Frankly, I would have immєdιαtely baptized the man, declaring "I have not found faith as strong as this in most of the Catholic Church."  In fact, this man had more faith than most Catholics, and, sadly, even more than Archbishop Lefebvre himself on this particular point at least.

There is a book "Tales of Foreign Lands" by rev. Spillmann, SJ , in the story "Maron" written in 1907 (available via Angelus Press),  where a young boy Ali lives along christians and slowly learns about the Faith. All the circuмstances are far from ideal, they constantly face death and prosecution. It it is a process, he professes the Faith first, a bit later actually refuses to be baptized and finally when he is ready he gets baptized. The author does not mention BoD or potential BoB, however the concept seems to be implied between the lines.
Also, it seems that the church never rushed the baptism itself, staying confident and full of hope that it is better to prepare  catechumens than later deal with partially formed souls. There must be the reason for that, moreover no fear of missing the train to the Salvation.
I have heard somewhere, that it is better for a soul of a good-willed-person to die without a baptism then be baptized and waste its life. This is why the church insists on full Catholic upbringing and refuses to baptize children where there are no prospects of a catholic environment.

In the Angelus Press book, "Preparation for Confirmation ", Part II, Section II, question 10.

10. Is Confirmation necessary for salvation?

Answer: Confirmation is not, unlike Baptism, ABSOLUTELY NECESSARY  for salvation. But all Catholics ought to receive it if they have the opportunity,  as it confers a sacrament.

Just can't make this stuff up......