It is interesting that Carl Barks made quite a few stories in which he incorporated the same type of crucial character, object or basic idea - but only in exactly three stories. Perhaps the most striking example is one of Barks' own inventions, Flintheart Glomgold (see more HERE), but other and much more general subjects emerging in triples are fairly easily found (burros and turtles as well as diamonds and submarines are diverse examples). Surely, Barks did not think of these 'trinities', but they nevertheless emerged during his long comic book career.
The sub-pages will present you to a small selection of these triple stories (which are not in any way connected), and in order to limit the numbers only stories starring Scrooge and/or Donald and the nephews are presented.