Scenario: Three transmitters A, B, and C report from a Companion. Each has separate later students, but only D transmits this particular report from B.
First observation: The report has several original routes, so it cannot be characterized as relying on one single early transmitter overall.
Second observation: D is isolated in transmitting this report from teacher B.
Conclusion: It is fard nisbi relative to the B–D link, rather than absolute singularity of the report as a whole.
If another reliable student of B is subsequently established, even that specific relative singularity will cease. Naming the relationship and checking all relevant routes are both essential.