I want to help, but I am unsure if I understand the issues you are describing. 

You say you have used Poser since Version 6, but much of what you are describing trouble with are basic Poser conventions that pre-date even Poser 6.

By "add to registry" do you mean adding it the Poser Library?  When unzipping or installing your Poser content are you making sure you are placing them in your Poser Rutnime Directory?

Since Poser 8/Poser Pro 2010 the Poser runtime is not locked to the software install directory and can be placed by the user, and it is recommended since Windows 7 to select a directory not restricted by windows UAC.  Because of this, when you start Poser after installation you need to point it to your Runtime.  This link may be useful:

https://www.posersoftware.com/documentation/13/HTML/Poser_Reference_Manual/BuildingScenes/Library/Adding_Libraries.htm

This video is for an older Poser version, but is also useful:

https://www.youtube.com/watch?v=YKVhCTcjLjI

Regarding who made the content in Poser - the content that ships with Poser has been created by a vast group of artists and content creators that has grown and expanded over almost two decades.  I am unsure of all of the current content with Poser 13, but in previous versions I know there were products and figures from Sixus1, Traveller, Vanishing Point, Meshbox, Zygote Media, Hivewire3D, Sanctum Art, just to name a few.  My own Runtime exceeds 3/4 of a Terrabyte and has too many content authors to be named.  I am unsure if there is a document or file available crediting all of the individual content contributors to the Poser Content that is sold with Poser. 

The New HD Toaster from Wamco toasts bread more evenly and acurately than Standard Toasters. Take advantage of the FULL resolution of your bread and try one today, because if your toast isn't in High Definition, you are not getting the most of your toast!