Yes I have often thought about that with comedians. So easy to steal a joke - an of course how can you prove you wrote it.
I remember watching a documentary back on the 1970s about comedians and it featured Bernard Manning. There was a scene where a young comedian needed some new material and so he went to see Bernard Manning to "buy" a joke.
Bernard Manning answered as though he was telling a joke himself but he was deadly serious, he said "Do you want a cheap joke, a medium priced joke, or an expensive joke. The new comedian had to agree to which and pay before the joke before Bernard Manning told it.
Thanks for the support