It's easy to spot the self-plagiarism in Disney cartoons when you're looking for it. Half the backgrounds from The Jungle Book pop up again in Robin Hood (which is one of my favorite Disney cartoons, but probably the most fraught with unoriginal material).

But this is pretty common in hand-drawn animation. Animators reuse or repaint cells to save money and time. It's usually backgrounds, which are less conspicuous, but not always. The most notorious were the Hanna-Barbara cartoons -- Yogi and Bubu or Shaggy and Scooby would run by the same background three or four times on a loop. The Simpsons have made fun of this more times than I can count, and they've done it themselves too. (There's an early Simpsons clip episode -- the exact one escapes me -- where Marge quite conspicuously makes the same gestures over and over again with different dialogue.)