F-Zero GP Legend (lost unaired episodes of 4Kids English dub of anime based on racing game franchise; 2004-2005)
F-Zero GP Legend (known as Efu Zero Farukon Densetsu in Japan) is a Japanese anime that premiered on October 7, 2003 on TV Tokyo, and ended its run on September 28, 2004. It lasted for a total of 51 episodes. It is based off the F-Zero video game franchise from Nintendo, and had it's own game based off the anime that was released around the same time.
A year after it's Japanese release, the show was dubbed in English by 4Kids Entertainment and premiered on the FoxBox block (later renamed to 4KidsTV) on September 4, 2004. Out of the 51 episodes that aired in Japan, only the first 15 episodes of the English dub were aired, since the show was cancelled, likely due to low ratings.
Most of the episodes that aired of the English dub is available online. However, it seems that there may have been more episodes dubbed than the 15 that have aired. The last episode that aired is "Target: Tanaka", which premiered three months after the episode before, on March 5, 2005 (and was shortly after the FoxBox was renamed to 4KidsTV). The following episode, "Super Scam", was scheduled for airing the weekend after on March 12, 2005, but was pre-empted for the second airing of Sonic X. Since then, F-Zero GP Legend has not aired again in the United States. Because episodes like "Super Scam" never aired, then that makes the episode unavailable to the public, and likely never will be. This leaves the fate of this episode, and the rest of the unaired English dub unknown. It's also unknown how many episodes actually were dubbed in English. The best estimate would be that all the Season 1 episodes might have been dubbed, or even less.