In the season 4's "The Weatherman," Marty Funkhauser says that his mother died ten years ago. However, as of the beginning of the season 6's "The Ida Funkhauser Roadside Memorial," Marty's mother had just recently been killed while driving her wheelchair.
In season five Richard Lewis has a set of golf clubs that he's so attached to that he won't loan them out, even to Larry who has just agreed to give him a life saving kidney transplant. In season six Larry and Jeff take Richard golfing and he knows nothing about the game.