When the War Machine is attacking the technician in the Post Office Tower, the machine has 2 guns attached. When the technician jumps into the machine, it has 1 gun, and when the camera changes again it is back to 2 guns.
Upon seeing the Post Office Tower, Dodo remarks that "it's finished," implying that it was not fully constructed before she left for her adventures with the Doctor. Construction on the Post Office Tower was completed in 1964, while Dodo left with the Doctor in 1966, two years after the tower was completed.