Different segments of a report need not all come through an identical path. A narrator may receive an opening passage through one chain and another section through a different chain. If only the first chain is given and the complete wording is transmitted as a unit, listeners will misattribute the later portion.
The distinction: Possessing more than one authentic source is not objectionable. Interpolation arises when the reality of distinct sources and hearings is obscured.
Illustration: A narrator hears the first two sentences from teacher A and the remainder from teacher B, yet attributes all four sentences to A. Once the separate hearing is established, the latter portion must be identified with its proper route, not automatically granted the strength of the first portion's chain.