An isnad may list outwardly upright and precise narrators and seem continuous, yet the report can fail as sahih li-dhatihi because of anomalous contradiction or a hidden disqualifying defect. Evaluation therefore proceeds beyond names and apparent continuity to comparison with other preserved routes.
Case A: Highly precise narrators, established reception, no credible contradiction, and no disqualifying defect: all conditions may be met.
Case B: All visible qualities remain, but stronger corroborated transmissions establish an incompatible narration and show where the narrator erred: the report fails through shudhudh.
Case C: The chain looks uninterrupted, but detailed analysis reveals a concealed break or attribution error: the report's grade is impaired by ʿillah.
Authenticity is the outcome of several joint conditions; a single favorable feature is never equivalent to the whole verdict.