If the application is not a multithreading or PL/I multitasking application, then the STACK statistics are for the one and only thread that executed, and the THREADSTACK statistics are all zero.
If the application is a multithreading or PL/I multitasking application, and THREADSTACK(ON) was specified, then the STACK statistics are for the initial thread (the IPT), and the THREADSTACK statistics are for the other threads. However, if THREADSTACK(OFF) was specified, then the STACK statistics are for all of the threads, initial and other.