Suppose a narrator is reliably known to have developed ikhtilāṭ after 200 AH. Three students report the same hadith.
Route A: the student heard it in 195 AH; later confusion does not directly disqualify that earlier hearing.
Route B: the student heard it in 205 AH; the route is affected by the narrator’s deteriorated retention.
Route C: the audition date is unknown; further chronological investigation is needed.
A fourth genuinely independent and reliable route supporting the content would invite a reassessment of the whole report. Thus even reports from the same teacher can differ in standing according to the condition prevailing at the time of hearing.