Not necessarily excluding written traditions, but referring mainly to oral tradition. Note the distinction between the many who attempted to draw up a narrative and the eye-witnesses and ministers who handed down the facts.
From the beginning (ἀπ' ἀρχῆς)
The official beginning, the commencement of Jesus' ministry. Compare Act 1:1, Act 1:21, Act 1:22; Joh 15:27.
Eye-witnesses and ministers
Personal knowledge and practical experience were necessary elements of an apostle. Eye-witnesses (εὐτόπται). Only here in New Testament. Peter uses another word, ἐπόπται (2Pe 1:16). Frequent in medical writers, of a personal examination of disease or of the parts of the body. Compare the modern medical term autopsy. Ministers (ὑπηρέται). See on Mat 5:25. In medical language denoting the attendants or assistants of the principal physician.