Why written records do not cleanly separate history from prehistory

Is prehistory simply the period before surviving written records?

That boundary is too narrow because history also uses oral testimony, archaeology, material remains, and forensic engineering; even cave art complicates the definition of a record.

Historians reconstruct the past from oral traditions, archaeology, objects, and engineering evidence as well as texts. The forensic-engineering example shows how equipment can be understood when its plans have been destroyed but the machinery and testimony from operators remain. A written-record boundary would exclude evidence that historians already use in ordinary practice. Cave paintings further blur any supposedly firm boundary between record and artifact. The label prehistory therefore imposes a boundary that the available evidence cannot sustain.