The popular Nickelodeon show has dealt with a lot of copyright issues, causing a lot of it to go unaired and/or not even available online. Most notably the Best Of episodes. Best of Episodes are when Sketch comedies such as Saturday Night Live and Robot Chicken go back on their best moments.
In 2001, only a year into All That's hiatus and re-tooling for Season 7, Dan Schneider signed a deal with Nickelodeon to prepare Best Of episodes during the hiatus. However, only cast members Josh Server, Kenan Thompson, Lori Beth Denberg, Amanda Bynes, and Danny Tamberelli returned to host them.
However, after the series returned in 2002, the Best Of episodes, despite being listed as official season 6 episodes were never noticed to air during re-runs of Season 6. In 2008, when Seasons 3-7 were re-run in a repeated cycle on The N, the Best Of episodes weren't broadcast.
These episodes currently can't be found anywhere.