A clear route to establishing fabrication is the fabricator's admission. Another route consists of external evidence making an alleged hearing impossible or deeply implausible—for example, a narrator claims to have met a teacher at a time when that meeting could not occur.
Chronological illustration: Someone claims direct hearing from a teacher who died before the claimant was born. If dates are securely verified and no alternative chain is being asserted, the claim is untenable.
Yet not every chronological anomaly automatically proves fabrication. A mistaken attribution, corruption of a chain, and intentional invention are distinct possibilities; an informed decision rests on the cumulative evidence.