A mastūr narrator, an irsāl, or an unclear link associated with tadlīs may lead to suspended judgment about one particular route. A credible, genuinely independent supporting path can justify reassessing the strength of the report as a whole.
But not all missing intermediaries are equally problematic, and combining two mursal chains does not automatically prove authenticity. The possibilities concerning an omitted narrator, the standing of the other transmitter, and independence between routes must be examined.
The principle is cumulative evaluation of new evidence, not concealing defects in individual isnāds or declaring every multiply transmitted report sound by default.