A transmission securely heard during the narrator’s earlier period of reliability is not rejected merely because the narrator later suffered ikhtilāṭ. The report still requires the other conditions of acceptance, but later deterioration does not retroactively invalidate demonstrably accurate earlier hearing.
Example: a student transcribed material from a teacher twenty years before that teacher’s age-related confusion. If the date of hearing and the student’s accuracy are established, the teacher’s final condition alone cannot justify rejecting the earlier report.
Therefore the chronology of audition and dates on which particular students met the teacher are especially valuable.