**Does the church actually teach that they are not condemned? **
What I recall was some polite phrase about hope for them.
Bear in mind that the Council of Carthage was a council of the local synod of the north African church. It was not ecumenical and not binding outside of the synod.
However, sometimes these synodal gatherings set precedents, much as in jurisprudence. Other synods could (and probably did) adopt a similar position later.
The Council in question is problematic, because local synodal gatherings/councils did not actually need or seek the approval of the bishop of Rome in those days. This one especially.
The common practice was to publish the findings of a Council and send them to other synods of the church. Naturally the bishop of Rome would get a copy like everyone else. If the other synods did not like what the local/regional Council did there was little they could do about it, unless there was a suspicion of rank heresy in the Councils statements, then they would start screaming

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Saint Augustine apparently called this “the Great Council of Africa”, the Archbishop-Metropolitan of the African Synod sat in Carthage, and he chaired the assembly. Saint Augustine would have taken part as a sitting member of the synod, with one vote like everyone else. He was already famous for his great debates with Pelagius the Celtic clergyman and his theory about damnation of the unbaptized. So it was this local council, among his friends and colleagues, that the idea was first formally adopted.