When Col. Wilder discovers the grave markers of Peter Hathaway's wife and daughter, the markers state that both died in July 2000 AD. Then when Col. Wilder tells Father Stone, he tells him they died in July 2000 AD. Father Stone says that's 7 years ago, which would make the current year 2007. In the following scenes they say it is March 2007.
According to the earlier episodes, the third expedition to Mars (the first successful expedition) did not reach Mars until June 2001, and the colonization fleet did not arrive until February 2004.
Hathaway speaks as if he served on the third expedition with Wilder, describing what Spender said about wanting Mars for the Martians. However, Hathaway wasn't on the third expedition shown in "The Expeditions." Parkhill and Wilder were the only survivors of that expedition.