The repair on the newly restored original Photos Library yielded vastly different results.
There were lots of new "empty" images added.
A few images were incorrectly "located" using position data from other images; can't seem to delete the erroneous locations, nor am I able to see or copy the correct location from images taken in the same place (even though Photos clearly shows where they were taken in their group headlines).
I did lose some images, and others had their thumbnails replaced with unrelated, usually distorted thumbnails of other photos.
It appears that almost all of the issues affected more recent dates (past 6 months), though the thumbnail issue occurred with one of my oldest images.
I'm viewing the source Photos Library that I copied to my Mac Pro to use as a comparison to the "repaired" Photos Library on my MacBook Pro.
I did notice that I've lost all "Live Photos" (those that have short videos included with the "static" image) and videos taken with my iPhone, even when I open the original source Photos Library on the original computer that it was maintained on. These were recent images from the new iPhone 6S I got in January, so it's not a terrible nor huge amount of lost memories.
The thing is, I'm not sure of the significance of these issues: was it truly corrupted images and/or database? Or is this indicative of systemic problems with the Photos app itself? Or is it with file system corruption, or the hard drive itself (SMART checks out clean bill of health)?
In the meantime, I'm going to continue using the "repaired" library and restoring each affected or missing image one by one. I would hope that the "repaired" library will not suffer the same problems if and when it needs to be repaired again...