The character of Princess Margaret is actually a composite of Henry's older sister, Margaret Tudor, and his younger sister, Mary Tudor. The events in the series are from Mary's life; using Margaret's name helps avoid confusion with Henry's daughter with Katherine of Aragon.
The "T" in The Tudors (2007) logo is three-fold: First, it's a "T" that stands for "Tudors". Second, in Christianity, it's the cross Jesus Christ was crucified on. And third, it's a sword pointing downward.
Steven Waddington's character, Edward Stafford, 3rd Duke of Buckingham, lays claim to the English Crown by being the descent of Edward II. In 1991 Steven Waddington played Edward II in Derek Jarman's film version of Christopher Marlowe's play Edward II (1991). Each of their claims to the English Crown were brought to a horrible end.
Actress Anna Brewster who portrayed Anna Buckingham in the first two episodes of the first season has been included (through a scene clip) in the first three season's opening credits. Before Henry Cavill's credit rolls, a distinct scene that both actors shared in the first episode of season 1 appears. The scene was not included in the opening credits for season 4.