Duranty got the prize for being one of a very small number of Western journalists allowed into Stalin's Soviet Union, and writing about a visit to Ukraine.

He made no mention of the mass famine ongoing at the time, the Holomodor. Wikipedia lists the death toll as "3 to 12 million", because it was a totalitarian state and real measurement was impossible.

So the answer to "is it possible for millions to die and it simply not be reported at the time" is "yes".