If a pupil is known to have heard a narrator after serious memory deterioration, that particular audition cannot be treated as equivalent to the narrator’s previously accurate transmissions.
However, two conclusions must be distinguished: the accuracy of this specific route is compromised and the reported content is unsupported by every other route. The first does not automatically entail the second. Another independent, sound chain may preserve the same content.
Thus criticism of a post-ikhtilāṭ transmission is a finding about that route; assessment of the matn as a whole still requires a search for other relevant transmissions.