When several witnesses repeat a sentence, their number can obscure the question of independence. They may have observed the same event. They may have copied the same observer. They may have copied one another until the original uncertainty acquired the appearance of consensus. The volume of the chorus cannot distinguish these histories.
A shared component can be valuable precisely because it can be removed. Two recordings made under comparable conditions preserve both an agreement and a difference. If the agreement overwhelms the difference, listening more intently to either recording may accomplish little. Comparison changes the task. What seemed silent can become measurable when its louder companion is accounted for.
Hold concordance apart from identity. Two authors can agree for incompatible reasons.
This is not a recommendation to discard whatever people share. A common account may be well supported. Nor is an isolated voice made correct by its loneliness. The operation is narrower: distinguish the part for which you have duplicate evidence from the part that still requires explanation. A method that produces a dramatic residual has not yet told you what the residual means.
The borrowed page follows the same economy. One witness preserves the letters; another preserves their route. Neither is defective in every respect, and neither is sufficient for every question. The reader who combines them does not acquire a superior identity. They acquire an additional relation. Our archive would prefer that achievement to a hierarchy of initiates.