Screenplay ideas were being written dating all the way back to 1991.
In the part where the animals are in the garbage truck you can see a sign advertising Radio Disney and another advertising for Kodak. There is also an advertisement of a theater showing The Lion King (1994) on stage when they are being chased by dogs.
None of the humans' faces were seen throughout the movie.
The first animated Disney film not produced by Walt Disney Animation Studios.
This is the biggest animated film ever produced in North America. Over four hundred animators were put in a large building to work on the film.