An African-American guard is seen in the American compound. The American armed forces were not integrated during this film's timeframe.
All the American flags that appear have 50 stars. The American flag did not have 50 stars until July 4, 1960, 15 years after the story ends and five years after the Allied forces left Austria.
It never occurs to the German officers to confirm Kaufman's identity by checking Smekal's dossier, which would likely contain a photo.