Factual error: When the British Ambassador, Lord Marbury, greets Abbey at her party, he tenders best wishes from "Her Royal Majesty", his Monarch. However, as Her official representative, Lord John should have been cognizant that the reigning British monarch is referred to strictly as "His/Her Majesty".
Factual error: Lord John Marbury says he is "the Earl of Croy, Marquess of Needham and Dolby and Baronet of Brycey." His title according to the British peerage rules would be "The Earl of Croy" and he would be called Lord Croy in conversation. Lord John Marbury would be what one of his younger sons also named John would be called.
Chosen answer: A really annoying innate lack of sense. My friends and family say the same thing all the time, and I'm endlessly trying to correct them. I think people just don't know any better and (ironically) couldn't care less that they're speaking incorrectly.