With all due respect, and I have a lot of respect for the saint, but St. Alphonsus blundered badly in claiming that BoD was de fide.
He based this on two sources, a letter from Innocent II (or III) ... can't recall which, and Trent's passing reference to a votum.
First of all, the letter of Innocent II was not infallible, as it was not addressed to the Univeral Church, but to a bishop. Second, he was not teaching anything but opining and saying he was following the authority of Augustine and Ambrose ... in other words, not exerting his own papal authority. And, most alarmingly for St. Alphonsus, that same letter declared that this "unbaptized priest" (a very strange situation) entered heaven immediately, and without delay, contradicting St. Alphonsus, who claims that temporal punishment remains after BoD (which is totally made up and has no proof from Catholic theology). So St. Alphonsus himself explicitly contradicted a source which he claims was dogmatic.
In a very similar letter to a bishop, Innocent III claimed that it was sufficient for a valid Mass for a priest to merely think the words of consecration. St. Thomas Aquinas rightly excoriated him for that. So why wasn't that infallible also?
As for Trent, a mere passing reference to a votum for Baptism in an expository section of Trent does not make it a definition. Trent clarified its definitions by issuing Canons, and a definition of BoD appears nowhere in the Canons of Trent. There's no definiton of what it is, what must be believed about it, etc. Even if you believe Trent is referrig to BoD here as a substitute for actual Baptism (I do not but believe that Trent was ... be back to that in a second), Trent is merely saying "it's not possible to be justified without the Sacrament or (at least) the votum for it." In other words, it's saying that must AT LEAST believe that a votum is required to not be a heretic, leaving the question open and undefined as to whether it suffices.
But Trent IMO is actually stating that BOTH are required, both the Sacrament and the proper intention/dispositions. There's actually a Canon which declares heretical the belief that the Sacrament of Baptism can justify someone who is not willing to receive it. I am absolutely convinced that Trent was teaching that both the Sacrament and the proper dispositions (votum) are required for justification. To say that something "cannot happen without" is a very curious expression that speaks to NECESSARY cause but not SUFFICIENT cause. While you can't bake a cake without flour and water, that doesn't mean you can bake one with JUST flour or JUST water. Flour and Water are both NECESSARY, but neither one by itself is SUFFICIENT for baking a cake.
Pope St. Siricius dogmatically declared that no one can enter the Kingdom of Heaven without the Sacrament even if they desire it. This is as close to a dogmatic rejection of BoD sufficing for salvation that can be found. I believe that the key here is to understand what the "Kingdom of Heaven" means. St. Ambrose declared that not even martyrs who she their blood for Christ can be "crowned" without the Sacrament, i.e. enter the Kingdom, even if he held they could possibly be "washed" by desire. That is where I hold that there can be a certain washing of the sensible punishment poena of sin by BoD, but not a crowning, i.e. entering the Kingdom, the Beatific Vision, without the Sacramental character that enables the supernatural faculty to see Go as He is (something which we lack by nature).
I hold that a martyr who shed his blood for Christ without the Sacrament of Baptism would go to Limbo, without any sensible punishment for sin and would enter a state of perfect happiness. Church decreed that in times of persecution the catechumens must be baptized even before they're ready. Why? If there's this dogma of BoB, then, well, if they died for Christ, they would go straight to heaven. What's the point of it?