The overall goal of my question is to understand how to fully control which components are used in a model, especially when saving a copy of it that I wish to alter, and either not alter any of the sub-assemblies or parts, or in other cases selectively re-use sub-assemblies and parts and alter others. I have used Save As with References, per the interesting Help article "Saving an Assembly in Various Ways," and some parts and assemblies do get copied and stored in the new location, but some do not. Baffling. And I've tried to change the referenced parts to designate the ones I want, per the article, Save As with References, and the changes I make don't stick, they revert to what was there before.
The screenshot attached shows one example of attempting to save an entire assembly and all its components to a new location but not all of them are copied to that location.
Thanks for the excellent help with past postings and this one.