Sub-process IDs for an un-archived parent process

Hi,

I am investigating an issue and need to unarchive some process instances as part of my investigation. I have the main process id and have un-archived that, but I need to find the process IDs for some of its sub-processes. I have written a process report and used the function sub_process_ids(), but it is not giving me any results. I know that there were some sub-processes instantiated because the process monitor shows that is the case.

Is there a limitation on the data that is returned by the function sub_process_ids()?

Is there another way I can find these sub-process instances?

Thanks in advance!