The term "Führerhauptquartiere" is written in plural which is correct in the English language. However, in the German language the word headquarters is written in singular when describing only one headquarters. So the correctly written form would be "Führerhauptquartier".
In the last "Grasshopper" movie Joe Blake is shown shooting prisoners with a Walther P-38 pistol. He cocks the hammer with his thumb every time he shoots. The P-38 is a semi-automatic pistol, meaning every time it is fired the slide cocks the hammer automatically.
The scrolling news ticker in the final scene (which depicts WWII ending as it actually did) begins with what appears to be "Mariner II reaches Venus", which occurred in December 1962, "ANC Leader Mandela arrested" which occurred August 2, 1962, and "Missiles In Cuba" which first became public in October 1962, all events which occurred months apart from each other.
When Juliana is telling the two resistance fighters about the last film she saw, she mentions an "A-bomb" explosion. Although the term "atomic bomb" was coined by H.G. Wells in 1913, the term "A-bomb" did not come into public use until after the bombing of Hiroshima (which doesn't happen in this alternate universe). In the alternate universe where Germany developed nuclear weapons first, it is known as a "Heisenberg device" (named after Werner Heisenberg who worked on the German nuclear project).
The sniper rifle used by the German to shoot the Crown Prince was a 'Dragunov sniper rifle', a weapon designed by the Soviet Union in the 1960s. As the Soviet Union was defeated during WWII in this timeline it's highly unlikely that such a weapon exists.