Corrected entry: If we assume the films are set somewhere between the seventeenth and eighteenth centuries, there would be no English Empire. After the Union of Crowns in 1603 and Union of Parliament in 1707, there would be a British Empire. (Note the Union Jack Flags which suggest this.).
Corrected entry: Keira Knightley wanted to kiss Johnny Depp so much, she begged the producers/director to add a kissing scene in which is the scene where she kisses Johnny Depp which leads up to him being handcuffed on the boat towards the end of the movie.
Correction: This is actually not true - the only things that Keira wanted in the movie was a) a sword and b) a swordfight. This is confirmed in numerous interviews and extras on the DVDs, and no-one has ever mentioned that she begged for that scene - even when asked, the scriptwriters etc. says that she didn't.
Correction: The producers have said that the films take place around 1740, therefore there would be an English Empire.
As original poster said 'After the Union of Crowns (1603), and Union of Parliaments (1707) there would be a British Empire' So the producers saying the film is set in the 1740's means that a reference to the English Empire in the film is incorrect, as the British Empire would have existed for 30+ years.