Right next to the Land Before Time, Winnie the Pooh is another old favorite of mine! LBT ultimately won my top spot due to my love of dinosaurs, but I'll always have a place in my heart for Pooh and his friends. Piglet was always my favorite character.
Yeah. He was never in the A.A Milne stories.
I believe one of Gopher's lines in the movie actually referred to that, where he said something like "you won't find me in the book," talking about the phone book in the context of the scene but also serving as an inside joke about the fact that he was a new character.