To Florus 2.212

Grace, however, is not conferred in the same way, repeatedly applied to each sin individually. Instead, poured in once, it wipes away many different crimes in a single concentrated action of its power. That is why he says, ‘From many offenses to justification’ (Romans 5:16): it leads human beings freed from many offenses to the glory of justification bestowed on them. Therefore he does not here mean Adam’s single sin, as you suppose. He uses the numbers one and many solely to praise grace: grace need not be repeated as often as each mortal person has sinned, as though individual baptisms could heal only individual sins.