After gathering evidence of fabrication, the classification may be based on overwhelming probability rather than certainty in every conceivable case. Even an alleged forger's confession could, at the level of abstract possibility, be a false confession; reliable indicators may still establish the practical judgment of fabrication.
«وَالْحُكْمُ عَلَيْهِ بِالْوَضْعِ إِنَّمَا هُوَ بِطَرِيقِ الظَّنِّ الْغَالِبِ لَا بِالْقَطْعِ»
The judgment of fabrication is generally reached by dominant probability, not necessarily absolute certainty.
Example: A person admits inventing a supposed prophetic statement. That is powerful evidence, but a careful investigator distinguishes a compelling practical judgment from metaphysical impossibility of every alternative.