This episode was originally produced for the second season. But Larry David was disappointed with it and postponed the air date. The airing included an introductory segment with Jerry Seinfeld explaining that there will be continuity errors.
When Jerry (Jerry Seinfeld) overhears Elaine (Julia Louis-Dreyfus) talking about her job at Pendant Publishing he exclaims: "Pendant, those bastards!" This is the same thing Elaine's father said when she told him she worked for Pendant Publishing in episode 2.3, The Jacket (1991).
Elaine's remark, "Maybe the dingo ate your baby," is a reference to the film "A Cry in the Dark," the true story of an Australian woman, Lindy Chamberlain Creighton, accused of murdering her baby. Chamberlain, played by Meryl Streep, claimed a dingo ran off with it.
Kramer (Michael Richards) first mentions the misadventure with the doves in episode 2.3, The Jacket (1991).
At the party, Ava asks George, "So guess who just sold 129 West 81st?" This is the address of Jerry and Kramer's apartment. The question also suggests that George is still working with Ava as a realtor, which makes sense, as the episode was filmed during season 2, apparently while George was still employed.