When a chain says that one narrator transmits from another, generational research first asks whether the two could even have lived at the same time. Being in the same generation does not conclusively prove an encounter, and belonging to different generations does not necessarily disprove every possibility of transmission.
Worked case: If A died in 180 AH and B was born in 190 AH, B cannot have heard A directly. If both were alive in 160 AH, coexistence alone still does not prove hearing; travel, location, explicit statements of audition, and other evidence remain necessary.
For a narrator known to practise tadlīs, chronological evidence helps identify where a concealed intermediary might occur. The final determination requires corroboration.