Let's try to look at the objective evidence and start with the Church Fathers. Dishonest articles like those by the CMRI, publishers of "The Salvation of those Outside the Church" ignore the Patristic evidence. Father Laisney had the mendacious temerity to claim that there was universal Patristic consensus in favor of BoD.
Hogwash.
We have about 5-6 Church Fathers explicitly reject Baptism of Desire, and several more implicitly rejecting it.
We only have 2 Patristic sources that allegedly accept it: St. Ambrose and St. Augustine, and all subsequent BoD theory relies upon the "authority of Augustine and Ambrose".
Well of these two, St. Augustine made some youthful speculation in favor, where after saying that he had gone back and forth on the question, stated that "I find ... [in favor of BoD]". Hardly something taught with authority as if it were received Tradition and Revealed truth. Unfortunately for those who rely on St. Augustine, he later retracted the theory, after his anti-Donatist and anti-Pelagian days, and issued some of the strongest anti-BoD statements in history.
St. Ambrose also was on record explicitly rejecting Baptism of Desire. What, then, of the apparent contradiction between that and his (ubiquitously-cited) Oration at the Funeral of Valentinian? In that oration, St. Ambrose did NOT claim that Valentinian could be SAVED by his zeal / confession / desire, but stated that like unbaptized martyrs, he could be "washed but not crowned". Crowning refers to entry into the Kingdom and Salvation. So this too is a false authority.
Pope St. Sulpicius explicitly and dogmatically taught and "each and every one" of those "desiring Baptism" would be lost if they didn't receive the Sacrament, or, rather, that they would forfeit the Kingdom and Glory (i.e. salvation and the Beatific Vision).
Even Karl "Anonymous Christian" Rahner had the intellectual honestly (lacked by most BoD Trads) to admit that the Patristic consensus was heavily AGAINST salvation by Baptism of Desire ... despite WANTING to believe the contrary.
There are only 2 ways to discern that some dogma/doctrine has been revealed:
1) unanimous Patristic consensus
2) some truth derives implicitly and necessarily from revealed premises
We see a big fat negatory on the unanimous Patristic consensus. In fact, the objective evidence shows the opposite.
And NO ONE has ever demonstrated how BoD derives necessarily from other revealed truths. We get long litanies of "Yep, BoD", "Yep, BoD" and ... "Augustine and Ambrose", "Augustine and Ambrose". That's IT, and as we see that Augustine retracted, while St. Ambrose did not teach salvation by BoD, the whole thing rests on a fallacious house of cards. St. Thomas came closest to providing some theological proof for it, but it was really more an explanation of how it worked than a proof of its existence. He said that the Sacraments have visible and invisible aspects to them, and that in the case of BoD, you get the invisible without the visible. That's not true of many Sacraments, in particular, of the character Sacraments. There's no such thing as Holy Orders of Desire (despite how much St. Therese desired to be a priest) or Confirmation of Desire. Those are two "character" Sacraments, where the character is an essential part of the grace of the Sacrament. Well, Baptism is also a character-conferring Sacrament. After BoD theory, the character was trivialized into a simple non-repeatability marker, a badge of honor that some in Heaven wore while others lacked, but which had no real effect. But the Church Fathers made it clear that this seal, this crowning, i.e. the character of Baptism was required for entry into the Kingdom and Glory (i.e. the Beatific Vision) ... even if some like St. Ambrose held that the other aspect of the Sacrament of Baptism, namely, the remission of sins, could be had by confession / desire.
Father Jurgens (pre-V2 Patristic scholar): “If there were not a constant tradition in the Fathers that the Gospel message of ‘Unless a man be born again . . . etc.’ is to be taken absolutely, it would be easy to say that Our Savior simply did not see fit to mention the obvious exceptions of invincible ignorance and physical impossibility. But the tradition in fact is there, and it is likely enough to be so constant as to constitute revelation.” (Jurgens, The Faith of the Early Fathers, Vol. 3, pp. 14-15, footnote 31, my italics)
“. . . we have to admit . . . that the testimony of the Fathers, with regard to the possibility of salvation for someone outside the Church, is very weak. Certainly even the ancient Church knew that the grace of God can be found also outside the Church and even before Faith. But the view that such divine grace can lead man to his final salvation without leading him first into the visible Church, is something, at any rate, which met with very little approval in the ancient Church. For, with reference to the optimistic views on the salvation of catechumens as found in many of the Fathers, it must be noted that such a candidate for baptism was regarded in some sense or other as already ‘Christianus,’ and also that certain Fathers, such as Gregory nαzιanzen and Gregory of Nyssa deny altogether the justifying power of love or of the desire for baptism. Hence it will be impossible to speak of a consensus dogmaticus in the early Church regarding the possibility of salvation for the non-baptized, and especially for someone who is not even a catechumen. In fact, even St. Augustine, in his last (anti-pelagian) period, no longer maintained the possibility of a baptism by desire.” (Rahner, Karl, Theological Investigations, Volume II, Man in the Church, translated by Karl H. Kruger, pp.40, 41, 57)
So much for BoD being revealed and so much for Patristic evidence for BoD.
After the Patristic era, St. Fulgentius, disciple of St. Augustine, rejected BoD, and that was the last any mention of it appears again in Catholic authors until the pre-scholastic period.
To be continued with the Pre-Scholastics (Abelard, Hugh of St. Victor, Peter Lombard) ...