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 (also available in DAZ and HiveWire3D flavours) 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.