In the climactic battle scene, a number of the Chinese peasants can be seen using Mauser 98k rifles, a variant of the 1898 Mauser which wasn't introduced until 1935, at least a decade after this film is set.
In the scene where they escape from the Arab camp, a young Arab man claims he will kill himself if she leaves. Eve screams... well, originally it was just "Men!" and he lips clearly say more. But the sound is blanked out. Otherwise, I guess it would have been a 15!
The wreck of first the deHavilland burned and the engine fell from its mounts. Both deHavillands were shown flying in the film and were powered with the V-8 Curtiss OX-5 powerplant. The engine seen in the burned airplane was an inverted inline 6 cylinder, most likely a Liberty 12A six cylinder.
Their "high road to China" takes them from Europe through the Middle East, Afghanistan, Nepal, arriving in China via the Tibetan highlands from the West. Using this route, it is impossible to fly over the Great Wall of China as indicated in the movie. The Great Wall is on the northern part of China.