unascertainable

This term conveys a sense of absolute epistemic limitation, where the lack of information is not merely a temporary hurdle but a structural impossibility. It is most frequently employed in formal, legal, or technical reports to describe data that cannot be recovered or verified regardless of the effort applied.

Because it describes a state of permanent uncertainty, it carries a colder, more clinical tone than words like unknown or mysterious. It suggests a failed attempt at verification rather than a simple lack of knowledge.