Luckily for Toobworld purposes, they never referred to the talking horse as a TV show. The only difficulty presented by his mention since they share the same TV dimension is that Ed and his "owner", Wilbur Post, tried to keep his ability to talk a secret. So how did Nate Ford and Co. learn about him?
Who knows what may have happened after the series ended? I don't know if Ed would have finally published his memoirs - it would have been a guaranteed best-seller. After all, how many talking horses ever escape from the Island of the Houyhnhm and come to live in the land of the Yahoo? But it could also be that someone finally discovered the truth and exposed Mr. Ed to the world.
And that's how Team Leverage knew about him.
If this had taken place in the sketch comedy TV dimension of Skitlandia, we'd know how Mr. Ed's story turned out. Until his death, Ed was a right-wing radio talk show host in North Carolina. We learned that from an unsold, but broadcast, pilot for a show called 'What's Alan Watching?' - which is where Alan Sepinwall got the name for his blog.