In season 4, episode 5, Marty Funkhouser is speaking at his father's testimonial. During his speech, he says that his mother died 10 years ago. However this episode is based around Funkhouser's mother's sudden death despite the fact that Marty previously claimed that she died more than 10 years earlier.
In Season 8 - Ep 8, Larry and Jeff decide to invest in an inventor who has created a car periscope. Larry David actually introduced this idea 15 years ago in an episode of Seinfeld - "The Invitations".