Terrorist groups don’t have formal rosters the way sports teams do. It is sort of like “former intelligence officer”. It is definitely a strong argument (strengthened by time and distance separation, degree of clear separation or renunciation, etc) but it would almost certainly cause delays and substantial extra investigation, if nothing else.
If you played for a team, you were a member of that team.
If 10 years after you leave, that team goes on to win the championship, you are not and were never part of a "championship team."