Scripting against existing case.

We have a “user event” script that executes against “new” inbound email cases.  It runs on the afterSubmit of the case.  We are attempting to add additional functionality and run some updates to the customer record when the case is updated.   These updates would come from a non NS custom form whose results are sent to the Case Reply To email address.

This is my problem.  I’ve tested and found the script does not run at all against existing cases, only new cases. This script was written by someone that is no longer with us and he vaguely remembers there was some sort of Preference or Switch that he used to only allow the script to run against new cases.  I cannot find any such preference or switch.  Would anyone know where I should be looking to allow this script to run against existing cases as well?