I also tried exporting one of my original test props as an OBJ, reimporting that, saving that as a new prop, and loading that.

Exported one of the Slicer swords as an OBJ, reimported it:

External Name = SlicerSword_3 (Internal Name = SlicerSword_3)

Saved as PP2

{
version
    {
    number 9
    }
prop SlicerSword_3
    {
    geomCustom 
        {
        ...
        } 
    }
prop SlicerSword_3
    {
    name    SlicerSword_3

New scene, deleted Andy, loaded 3 of theses

External Name = SlicerSword_1 (Internal Name = SlicerSword_3)
External Name = SlicerSword_2 (Internal Name = SlicerSword_4)
External Name = SlicerSword_3 (Internal Name = SlicerSword_5)

New scene, loaded 3 of these (not smartprops!), parented each to Andy,

External Name = SlicerSword_1 (Internal Name = SlicerSword_3:1)
External Name = SlicerSword_2 (Internal Name = SlicerSword_4:1)
External Name = SlicerSword_3 (Internal Name = SlicerSword_5:1)

The 3Dcheapskate* occasionally posts sensible stuff. Usually by accident. And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU or something else.
*soon only to be available in two flavours - DAZ and Renderosity

Forum: Poser - OFFICIAL

Subject: Why Does the External Name For A Prop SOMETIMES Have An '_1' Suffix