A back of the old envelope shows that once you’ve accounted for first generation foreign-born mothers and mothers who had children with non-black fathers and label them black, from the maternal side at least, married non-Hispanic black birth is about 50-60% native-born. This means that the 80%+ unwed numbers I’ve seen thrown around in some black parts of the interwebs have some anchor in reality. That is in fact pretty close to the native-black unmarried birth percentage. Immigrants have a 40% out of wedlock birth rate, which necessarily means the non-immigrant out of wedlock birth rate must be higher than 70%. Hispanic black birth is 65% or so unmarried, and so doesn’t shift the native rate that much.
Without the substantial and parallel increases in outmarriage and immigration keeping births relatively stable year to year, the native-born black TFR is somewhere down in the dumps like the Native American one, about 1.4 or 1.5.
This explains a lot.