Wikipedia:Don't say something is unknown just because you don't know

You will come across articles where someone will assert that a certain fact is unknown. Before you write in an article that a certain fact is unknown, consider if the fact is unknown to you or unknown to the body of collective human knowledge.

If the answer is the former, then please, don't write in this encyclopedia that the fact is unknown.

Your ignorance (perhaps despite some research) does not make it a fact suitable for inclusion in this encyclopedia. By stating that it is "unknown" when someone, somewhere knows the answer is deliberately adding false information to the encyclopedia. WP:Editing Policy clearly states, "on Wikipedia a lack of content is better than misleading or false content."

If the fact is truly unknown, then cite that it is unknown with an inline reliable source.