From Planimate Knowledge Base
Any subsystem can create an object label reference for its owning portal using the routine operation Label->Create SubSystem Label.
This is very useful in cases where a parent portal has been dynamically copy/pasted and a portal contained therein needs to also be referenced using an object label reference. A routine executing within this other subsystem can allocate and obtain a label reference for that subsystem and store it in an attribute, in effect creating a "handle" to that subsystem.
This helps avoid having to copy/paste systems in layers in order to get label references to subsystems deeper in the hierarchy which is copy/pasted.
idkbase note 43