During Violet and Rose's talk the left side of Rose's necklace changes position repeatedly.
In reality, a second footman like Alfred would have been sacked on the spot after calling the police on Thomas without gaining permission from Carson, who in turn would have needed the okay from Lord Grantham. Having law enforcement officers interrupt the cricket match to question a servant right in front of the villagers would have been humiliating to the family, a transgression that would have been unforgivable.
Mrs. Bates' Sewing machine is set up backwards.
The Earl refers to infamous Charles Ponzi's pyramid scheme as an ongoing chance for investment. In reality, the original "Ponzi Scheme" became insolvent in 1920, the previous year.