(global boolean BACKTRACK false)
(script startup BACKTRACK_TOGGLER
(sleep_until (volume_test_objects FINAL_TRIGGER_VOLUME (players))
(set BACKTRACK true)
(script continuous triggertester
(if (volume_test_objects TRIGGER_VOLUME_1 (players))
(PLACE SCRIPTS HERE)
Replace the trigger volume names with your own volumes. What this does is create a global with the value of a boolean, and sets it to false. Then when the player goes through the last trigger volume, it sets backtrack to true. Now any trigger volumes that are passed through while BACKTRACK is true will go through the commands you put under (PLACE SCRIPTS HERE). If BACKTRACK is not true (the player didn't reach the final volume), no commands will play.