Default scene with Andy, loaded four SlicerSwordLH's (smartprops, same sword as my earlier examples). My script gives this data for the 4th Slicer:

External Name = SlicerSword_4 (Internal Name = SlicerSword 3:1)

I saved the prop both as smart and non-smart:

Saved as non-Smart:

{
version
    {
    number 9
    }
prop SlicerSword 3:1
    {
    storageOffset 0 0.3487 0
    objFileGeom 0 0 :Runtime:Geometries:VaL_Slicer:SlicerSword.obz
    }
prop SlicerSword 3:1
    {
    name    SlicerSword_4

Saved as Smart:

{
version
    {
    number 9
    }
prop SlicerSword 3:1
    {
    storageOffset 0 0.3487 0
    objFileGeom 0 0 :Runtime:Geometries:VaL_Slicer:SlicerSword.obz
    }
prop SlicerSword 3:1
    {
    name    SlicerSword_4

Not conclusive, but a good indication that the :1 internal-name suffix and the _1 external-name suffix when you save a parented prop are what was present in the scene.

My current guess on when the :1 suffix appears is that it's added when you parent a prop to the figure, and the value of the suffix will probably be the same value as the suffix for every actor on that figure. Time for a test.

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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