Muttafiq and muftariq: identical names borne by different persons; the task is to avoid conflating transmitters.
Muhmal: the chain does not distinguish which of several similarly named teachers is intended; the task is identification and assessment of the ambiguity.
A teacher's denial of a report: contrasts the student's positive account with categorical denial or failed recollection; the task is to decide the reliability of that attribution.
Musalsal: repeated verbal or practical features across stages; the task is to describe a mode of transmission.
Together these address different questions: who is this person?, which namesake?, who remembers the hearing?, and how was the report passed on?. The answer to one cannot substitute for proof of another.