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* 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