What is an acceptable form for a "no" answer to a question of the form "Does X exist in the lore?"

Question

This question asks whether there is an "in-universe" explanation for a particular piece of lore in a particular setting. Note that there is already a meta question about the question's topicality. The appropriateness of the question aside, how does one provide an acceptable answer to such a question if the answer is "no"?

As it happens, the lore question that occasioned this meta question is susceptible of a "yes" answer, and one was eventually posted. But the larger problem remains. If there is no clear "yes" answer to a question of the form "Does X exist in the lore," then the answer requires proof of a negative. As far as I know, the only way to prove a negative is by inductive reasoning. Induction depends on supportive argumentation to make its probabilistic conclusions more probable. Where the question demands that an answer rely on in-universe sources, and no such sources exist from which to argue, what is the best practice? To provide information the querent might find useful even if it doesn't actually answer the question? To simply leave the question unanswered indefinitely, as suggested here? Something else?

Reviewing other potentially related meta questions, I observe that the querent wasn't asking about the existence of a product, but the issues raised seem similar.

Answer 1

The well-received “no” answers I've seen followed this kind of pattern:

No, that lore tidbit isn't defined anywhere. I have read this vast swathe of material about this setting [like most of its novels and supplements]. Based on my experience, if the answer was anywhere, it would be in these specific books I'll name/describe, all of which I have read and double-checked for an answer. There is no answer in any of those about this.

This gives us a pretty good idea that you've gone to good efforts to check all reasonable sources and found nothing, which is close enough to a “no” for many people. It's not 100% comprehensive and it's not 100% guaranteed but it's pretty good.

Someone may answer with a “yes” later, citing a source this previous answerer had overlooked or citing a single paragraph in one of the books they'd checked (but they'd missed or misread that paragraph). This is OK.

There's a lot of work involved in this kind of answer. Nobody is obliged to do it.

It is OK to leave a question unanswered. If you don't know of a “yes” and can't prove a “no”, just leave it for someone else. Eventually we'll get a “yes” with a good citation, or a good-effort “no”.

I do not recall ever seeing an attempt to prove a “no” without the bookreading effort backing it up that has been received well.

Answer 2

Answering "no" is not an excuse to give purely opinion answers

@dopplegreener answered what to do to make a good "no" answer. I wanted to add at least one thing that good "no" answers should not do:

No, X does not exist in the lore. So now I will spend the rest of my answer telling you what I think the lore would say but I can't prove or substantiate any of it. These words sound good and make sense but none of them are drawing from lore. But that is ok because the lore says nothing so a best guess is better than nothing.

This kind of answer is not acceptable. We saw this issue all the time with designer intent questions and we see it a lot with "Does X exist" questions as well. Just because there is no clear answer does not give license for people to give straight opinions and call it an answer.

If a question is asking for lore, the answer should explicitly draw on lore or other tightly related sources. If there is no lore-based information about the topic to draw off of, then either do as dopplegreener said in their answer or just don't answer at all. A pure opinionated guess (no matter how educated) is never better than nothing. We actually prefer nothing over low quality answers.

The long and short of it is that if you don't have the information to back up your answer (either "yes" or "no") just don't answer.