Some writers claim that the Eugenics War was actually a type of "Cold War" or underground, fought between nations while the general population was unaware. That accounts for the absence of reliable "records".
Also, the USA was not involved in the Eugenics Wars, so it's not surprising that the visits to the past (most of which did indeed involve the US) didn't depict it.
It is by caffeine alone I set my mind in motion. It is by the beans of Java that thoughts acquire speed, the hands acquire shakes, the shakes become a warning. It is by caffeine alone I set my mind in motion.