Comment by otabdeveloper4

> previously unencountered problems

I haven't read the IMO problems, but knowing how math Olympiad problems work, they're probably not really "unencountered".

People aren't inventing these problems ex nihilo, there's a rulebook somewhere out there to make life easier for contest organizers.

People aren't doing these contests for money, they are doing them for honor, so there is little incentive to cheat. With big business LLM vendors it's a different situation entirely.