At the beginning of Elizabeth's meeting with Tony Blair, she refers to Diana as "Princess Diana". While Diana was colloquially referred to as such in the media, it was an incorrect style because she is not a princess by birth and not entitled to use a princess title with her own name. Elizabeth, of all people, would know this and would never refer to her by this style.
Camilla smokes cigarettes in real life, but for some reason in this season she smokes only rarely. Silly.