«وَبِكَثْرَةِ طُرُقِهِ يُصَحَّحُ»
With a sufficient multiplicity of corroborating routes, the report can attain the grade of sahih.
The standard case of sahih li-ghayrihi starts with a report that is already hasan li-dhatihi through one acceptable isnad. Relevant, sufficiently independent corroboration can raise the report's total evidentiary strength to sahih. It is called li-ghayrihi because the higher grade does not arise from the precision of that lone isnad in isolation.
Multiplicity is not an automatic certification. The supporting routes' reliability, independence, agreement, and freedom from decisive contradiction must be assessed.