But the can say "I don't know." They can be trained to do so ("as of my knowledge cutoff in September 2020 I don't know who Bob Whatgenflabl is") and they can b

But the can say "I don't know." They can be trained to do so ("as of my knowledge cutoff in September 2020 I don't know who Bob Whatgenflabl is") and they can be given context that makes it more likely they do so (I've had good success with this for RAG applications, and extremely little, but not zero, for general prompts.)