Fard and gharib primarily describe the distribution and isolation of transmitters; sahih and daʿif evaluate the report's overall reliability. Singularity therefore does not by itself justify rejecting every such report.
Conversely, saying that only one person transmitted a report does not excuse investigators from examining that narrator's accuracy, integrity, the continuity of the chain, or possible defects. Singularity is a reason for focused scrutiny, but its impact depends on the evidence of the specific case.
Crucial distinction: “This report is fard mutlaq” describes chain structure.
“This report is sahih li-dhatihi” evaluates whether defined conditions of acceptance are met.
The formal criteria of the second subject will be taught in the following lesson.