At Fry's 8th birthday party, his father asks if he's worried about America's "boys in Grenada." This implies that Fry's party occurred between October 25th and November 2nd of 1983, and thus, Fry was born on the same date in 1975. But Fry is stated to be 25 years old on December 31st, 1999, so he would have to have been born in 1974.
An alien uses correct grammar (a predicate nominative) when he says, "It was we," but another alien commits a hypercorrection by saying it should be "us."