Poser doesn't save multi-props as smart props, a bug since Poser4.
Poser only save as smart prop a single prop.

To make a multi-part prop smart prop you must do:
1- Select all the props and sve them in the prop library. It doesn't matter if the root prop has a parent or not, Poser always will save it as without parent.
2- Once saved, with a text editor find in the pp2 file the root prop and change the line

parent UNIVERSE  by smartparent your body part

ex: smartparent Head
    smartparent rRing2

In this way you can make every prop parented to a different body part, for example, loading a single armor prop you have each armor part parented to its respective body part

Stupidity also evolves!