I had a new thought on the problem and found what was going on.
The PRC script calls this script as part of the NPC death event:
ExecuteScript("prc_pwondeath", OBJECT_SELF);
I did not have that script anywhere in the module, so I added it with this code to call Shayan's XP script and it is now working.
prc_pwondeath:
void main()
{
ExecuteScript("sha_xpsystem", OBJECT_SELF);
}