The working production Title was MI6 based on the highly secretive British anti Nazi group during WWII, which was so secretive it wasn't even acknowledged until the 1970s.
Writer and director Hailey Jackson chose the name David as a tribute to one of her favorite movies, American Werewolf in London in which the lead character, David becomes the monster he hates most. Also a tribute to king David who took on the giant Goliath, and lastly David, a character in the book series "Uglies" written by Scott Westerfeld who is a leader of the rebel group outside the corrupt government driven city.
The name Cecilia was chosen as tribute to one of Hailey Jackson's favorite songs, 'Cecilia' by Simon and Garfunkel, as well as a tribute to Saint Cecilia who died as a martyr for her beliefs.
The Suit in the interrogation states "The day for individual happiness has passed" this is a direct quotes from Adolf Hitler.
Cecilia says, "It is not strange to mistake change for progress" which is a direct quote from President Millard Fillmore.