Same query was posted

on the DAZ Poser forum - http://www.daz3d.com/forums/discussion/77836/why-does-the-external-name-for-a-prop-sometimes-have-an-1-suffix/p1
on the CGbytes Poser forum - http://www.cgbytes.com/community/forums.aspx?g=posts&m=125261
on the RDNA Poser forum - http://forum.runtimedna.com/showthread.php?104756-Why-Does-the-External-Name-For-A-Prop-SOMETIMES-Have-An-_1-Suffix
on the Renderosity Poser forum - https://www.renderosity.com/mod/forumpro/?thread_id=2901360

A couple of unrelated observations that other folks made on some of those threads inspired me to try a few tests, which are documented on the Renderosity thread ** (if a moderator decides that those URLs aren't permitted just let me know and I'll delete them. Note: it's only Renderosity where I have to say that)**

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.

Forum: Poser - OFFICIAL

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