It is weird that people are brushing that aside. Stealing jokes is the greatest sin in comedy, and Rudy stole (well technically paid for) his whole act.
What I gathered was that these were apparently well known street tales and myths that ALOT of the older guys went around telling. Rudy just happened to know one of the older guys who could recite the stories in a comical way and went from there.
It would be like somebody doing Mother Goose rhymes. Nobody knows exactly who started it.
And Rudy refined and expanded the stories as he got more famous.
At least thats what I GATHERED from both the movie and reading up a little on Rudy. Doesn’t seem he like he stole original stories from one man