That was my thought as well. Every time a major contemporary comedian dies, someone mentions their valuable estate's huge files of thousands of jokes. Bob Hope and Joan Rivers come to mind.
Hope and Milton Berle had a huge feud about this and Berle was known as an outrageous joke stealer.
Abbot & Costello and the Three Stooges did some of exactly the same skits.
Charlie Chaplin STOLE ( and claimed it as his own idea and is now well known for ) the forks in potatoes dance; however, Chaplin STOLE that from Stan Laurel, when they both were doing English Music Hall and Laurel was THE bigger one/a headliner and it was something that Laurel originated and was well known, all over the UK, for!
Then there is JOE MILLER'S JOKE BOOK ( a very old comedian, who did publish his jokes ) and whom many comedians, after him, stole from.
Even Flip Wilson stole his "HERE COME THE JUDGE", from an old Burlesque skit.