Man ḥaddatha wa-nasiya refers to cases in which a teacher previously narrated a report but later forgot doing so. Hadith critics collected such occurrences as a distinct topic; al-Dāraquṭnī is mentioned in connection with a work on it.
Two points matter: first, a valid past hearing may remain documented despite the teacher's lapse; second, the teacher might even learn of his earlier narration from his own pupil and subsequently transmit it through that pupil.
This historical category illustrates the transmission process. It is not an automatic proof that every forgotten narration is sound; reliability, precision, and corroborating evidence still govern acceptance.