In his opening narration, Gen. Ten Eyck (Louis Calhern) states, "This is spring, nineteen hundred and forty-three." A few moments later, however, Gen. Larraby rides up to his office and when a soldier says to him, "Lovely day, isn't it?", he replies, "Yes it is, and October too." (And a day or so later, the German radio announces it will execute Dutch hostages the next day, October 21.)
When The Scarf is drawing a map near the end of the film, he uses his left hand and keeps his right hand at his side. However, in the closeup of the map his right hand is holding the paper down while his left hand draws it.
When Victor Mature's stuntman climbs up onto the balcony of German headquarters, the knot on his trademark scarf is pointed to the left, but in the subsequent closeup of 'The Scarf', the scarf's knot is pointed to the right.
Wounded Dutch resistance leader 'The Scarf' (Victor Mature) is held in a German hospital from where he's rescued by Peter Deventer (Clark Gable). with a heavily bandaged chest and his right arm strapped up and wearing a blue dressing gown he's shown off as a hero to the Dutch people from a hotel balcony by the colonel. When they re-enter the room, The Scarf's right arm has healed, as it's now unstrapped and in the previously flapping arm of the dressing gown. He must have taken a turn for the worse, as a short while, later his arm is strapped up again.
The cargo/troop planes shown dropping British paratroopers on Arnhem in 1944 are either C-82 Packets or its descendant the C-119 Flying Boxcar, both of which became operational after WWII.
The dresses and hairdos that Turner and other women wear are from 1954, not from the time of WWII.
Colonel Deventer goes into the road as the soldiers who have escaped from Arnheim come marching past whistling the tune 'Bless 'Em All' only the soldiers aren't whistling.