Count information paths, not documents
Three documents can repeat the same original statement. Their number does not automatically make the statement independently supported. Ask how each source learned the information. A newspaper summary, an office note and an interview may all trace back to one witness. They remain useful for understanding how a story spread, but they do not necessarily provide three separate observations of the event.
Worked example: the repeated departure
A fictional report says a boat left at dawn. A later interview repeats the report, and a memorial booklet quotes the interview. If none includes a direct observation or an independent departure record, the three sources form a chain. A harbor log created for another purpose could add a different information path, provided its entry actually describes the departure you are investigating.
Draw the source chain
Write source A repeats source B wherever the relationship is explicit. Leave uncertain dependencies marked rather than assuming independence. In Somatry, this helps you avoid becoming overconfident because a claim appears frequently across the file. The strongest comparison is not always the one with the most documents. It is the one in which distinct, relevant sources support the same narrow fact without silently borrowing that fact from each other.