It is my understanding that only those converts to Catholicism from Protestant sects that have probable valid baptisms, have to go to confession before receiving their first Holy Communion. Converts from other religions or atheism do not have to go to confession before their first Holy Communion because they are baptized by water beforehand, on the same day.
Yet it seems to me that if there was a such thing as baptism of desire, then all converts, even those from non baptizing sects, should have to go to confession before receiving first Holy Communion; because how would one possibly know or not if they received baptism, by their desire, months or years before they finished their Catechism instruction? What if the convert received baptism, by desire, when they initially started going to the rectory to receive religious instruction from the priest. Is not likely, or at least possible, that this convert might commit a mortal sin during the several months it takes to be instructed in the Catechism? If so, wouldn't this convert be in the same situation as a Protestant convert who has fallen into sin after his probable valid baptism, and whom has to go to confession before receiving first Holy Communion for precisely that reason? If one has received baptism, by their desire, and then commits a mortal sin afterwards before finishing Catechism instruction, I do not see how they are any different then the Protestant convert who has committed a sin after his likely valid baptism that he received in the Protestant sect.
Or is baptism of desire of such a different nature than baptism by water and the Holy Ghost, that it is not really worth being called baptism?