A viewpoint has boundaries
A narrator can describe an event sincerely while misunderstanding its cause, date or significance. Limited access to information is not the same as an intention to mislead. Ask what the speaker could observe, what they learned from others and what they are interpreting afterward. Those boundaries help you understand the account without reducing the character to either perfectly reliable or wholly untrustworthy.
Worked example: an empty berth
A relative remembers a boat's berth as the place where a loved one always returned. The account may omit a sale or a later change of ownership because the relative did not know about it. A marina ledger can establish the transfer while the memory remains emotionally accurate as a description of what the place meant to that person.
Let accounts contribute differently
When two sources disagree, identify the exact factual conflict and the different perspectives around it. Do not discard every useful detail from one account because another corrects a single point. In Somatry's short fiction, these differences often produce the mystery itself. In a case file, the same habit helps you evaluate interviews precisely: challenge the claim the evidence challenges, while keeping unrelated observations available for their own separate comparison.