Polycarp had personal acquaintance with eyewitnesses of our Lord's ministry.
Polycarp used a combined Old Testament + New Testament quotation and refers to them as "these Scriptures" in Epistle to the Philippians 12:4, marking a clear distinction between church writing and authoritative Scripture that was recognized within the church.
(The Origin of the Bible: Newly Updated by F. F. Bruce, J. I. Packer, Philip W. Comfort, and Carl F. H. Henry, 2020. The Canon of the New Testament by Milton C. Fisher, 71.)