First route: Qutaybah ← Jarīr ← Mughīrah ← al-Shaʿbī.
Second route: Abū ʿĀmir ← Abū Usāmah ← Mufaḍḍal ← Mughīrah ← al-Shaʿbī.
They converge on Mughīrah. Comparison can test transmission above that common point, but it cannot multiply the number of independent original witnesses.
Where critical wording differs, precision, collateral routes, and context determine whether the difference is expressive or substantive. Counting chains alone does not decide.