In Episode 5.01 of course we see Robert and Cora Crawley celebrating their 34th wedding anniversary, in 1924. However in Episode 1.01, set in April of 1912, Violet Crawley says to her son: "Twenty-four years ago, you married Cora against my wishes for her money!" This fact would mean that Robert and Cora were married in 1888, and would be celebrating their 36th anniversary in 1924, and not their 34th.
Martha brought Cora over in 1888; Cora was 20, recently out of school. She and Robert were engaged in 1889 and married on the 16th February 1890. That's all. The Series 1 date is cancelled out by later and more canon information.--HarryPotterRules1 (talk) 02:05, January 8, 2015 (UTC)