At the beginning of the movie, Mangal has the vermilion mark on his forehead. Later, while they wait for a new executioner, Mangal sits in the jail cell with no markings on his forehead. Then Heera comes and places the vermilion on him. Since this happens after the initial scene, Mangal's forehead should have been clear in the beginning.
When the opening credits roll, a coin can be seen on which there are the following words "Victoria Empress". The events of the film are set in 1857, but Queen Victoria becomes Empress of India by the decision of the British Parliament only in 1876 and this is announced in India in 1877, 20 after the story of the film. It is important, because the Mughal Emperor (Bahadur Shah II), still alive in 1857, is also shown in the film, and the British Queen gets this title long after his deposition in 1857 and his 1862.
The British forces are using an outdated form of shako. The form of shako used in 1857 had a top that was wider than the bottom.