Henry VIII refers to the James V, King of Scotland as his nephew. While this is historically true, Season One changed this by combining Henry's two real-life sisters (Margaret, Queen of Scotland and Mary, Queen of France) into one sister who married the King of Portugal. In the fictional universe of The Tudors, Henry VIII has no such relation to the Scottish monarch.
Margaret Pole (The Countess of Salisbury) was not executed until 1541, one year after the execution of Thomas Cromwell (06/28/1540).
When Sir Francis Bryan and his company are searching the Poles' house, they come across what is purportedly a 'Plantaganet banner' - it is more likely that is a Tudor banner, as it was the Tudors who united both the white and red roses of the Houses of York and Lancaster for the first time to symbolize the union of both houses through the marriage of Henry Tudor and Elizabeth of York.
When Francis Bryan is searching the Poles' house for evidence of conspiracy to overthrow the king, he and his associates come across what is supposed to be a 'Plantaganet' banner - This is most likely an error, as it was most likely the Tudors that first brought the red and white roses of the Houses of York and Lancaster together to symbolize the end of the Wars of the Roses and the union of both houses through the marriage of Elizabeth of York and Henry Tudor.
George Boleyn marries Jane Parker sometime after Thomas More's death (which occurred in 1535). In reality, George and Jane had married in 1525, a decade earlier than shown.