A ṭabaqah is a relative scholarly and chronological grouping, not necessarily a rigid numerical category of exactly equal ages. Birth and death dates, residences, travels and teachers’ active periods help establish whether a meeting was possible.
Contemporaneity (living in the same period), possibility of meeting (historical opportunity) and proved hearing (credible evidence of direct reception) are different evidentiary levels. If a teacher died in 200 AH and a pupil was born in 190 AH, that fact alone does not establish direct hearing.
A geographical affiliation does not show that a narrator remained there permanently; scholars traveled to receive reports. Biographical dates, locations and journeys must therefore be combined with explicit transmission wording and other indications when assessing a chain.