Dueling Movies: The 1980s was a very tumultuous time in animation. Don Bluth had very publicly split with Disney and started his own studio, which naturally was in competition with Disney. Oliver had two rivals from Bluth: The Land Before Time, which came out on the same day; and All Dogs Go to Heaven, released the following year but also featuring a roguish talking dog and a heartwarming little girl. Oliver did better than either in theaters, though it's now a somewhat forgotten member of the Disney canon while The Land Before Time and All Dogs Go To Heaven went on to spawn long-running video franchises.
What Could Have Been: Originally this movie was going to be a pseudo-sequel/spinoff of The Rescuers that followed Penny after she was adopted. You can still see some traces of it. (namely the main character's name being changed to "Jenny").