A key question is whether an independent supporting transmission can improve the standing of a weak route. Certain mildly deficient chains may be strengthened by a credible mutābaʿah or shāhid, provided the support is sufficiently independent and reliable.
This does not apply indiscriminately to every weak report. An established fabrication, a severely discredited source, or another major defect cannot be repaired simply by accumulating similarly defective or derivative versions.
The governing requirement is to identify the provenance and standing of the supporting route and its actual agreement with the original. Multiple chains only help when they offer meaningful evidence rather than repeating the same error.