The designation mahfuz can rest on superior accuracy, a larger group of credible independent transmitters, or other effective grounds of preference. Such factors matter when genuinely conflicting versions require comparison.
A narrator may enjoy a high general standing yet be less accurate in a particular teacher's reports. Conversely, several independent skilled pupils agreeing on a wording are a substantial indication, while numbers that merely multiply one shared error may be less compelling.
General principle: a report is not mahfuz merely because its meaning seems appealing. It is mahfuz when the evidence of transmission establishes its relative strength in the dispute.