In adults, one cannot be justified without desiring Baptism. If you read the Council's declaration on Penance you'll see that when the Desire for the Sacrament is all that is necessary, the Church takes the time to fully explain how. If the desire for Baptism were all that is necessary the Church would have explained it that way. Instead they have Canons stating that this is heretical opinion.
Yes, I think this is a good point. Why didn't the fathers of Trent take the time to say "Sometimes God can provide the grace of justification before the reception of Baptism to those who desire Baptism and have perfect contrition for their sins. This is called Baptism of Desire and it brings justification to those souls who receive it although it does not remove the temporal punishment due to their sins. And sometimes God can provide the grace of Baptism to those who die as martyrs for the faith before they receive Baptism. This is called Baptism of Blood and those souls who receive it are justified and also have all the temporal punishment due to sin forgiven so that when they are martyred they go straight to heaven." If they had only said something like that we wouldn't have to have all these endless arguments and accusations of heresy because everything would be clear. And for the Feeneyites here, why didn't the Trent Fathers just say, after they said that "Baptism is necessary for salvation" that "If anyone believes that souls can receive justification before Baptism by their desire for the sacrament and their contrition for their sins, let him be anathema. And if anyone says that souls can be justified by dying for the faith without receiving the laver of regeneration, let him be anathema." I don't know for the life of me why the Church didn't do either of those things. This argument must have come up before because there were those who believed in BOD and BOB and those who denied them from the beginning of the Church.