Yes, his death did atone for every human before and even after his human life on earth. Jesus is the Logos Creator of all creation, including all humans. Adam sinned and the consequence of “second death” has been imputed to one man and this particular sin of Adam, i.e., not any other’s sin. Because of Adam’s sin, “second death” (which is future) came to all, so therefore to atone for that sin of Adam(and all), only one person needs to die as a PASSOVER LAMB, the Messiah Jesus. See 2 Corinthians 5:14, 21;1 Corinthians 15:3; Romans 5:6, 12,17-19; Rom 6:23 And, this is a mechanism of atonement that has been planned prior to creation. Subsequently, this plan was activated and implemented at the death of Christ. From then on, humanity can claim this imputation of Jesus’ death for everyone’s sin. And, if, according to some scientists, there may have been humans before Adam, even those humans ( all sins imputed to Adam and death of Christ imputed to all) are “covered by the blood of the Passover Lamb.