This post contains a video, for a full easy explanation of my situation.
Video
https://www.youtube.com/watch?v=sThVzs0Q5pc&feature=youtu.be
The Issue in a Nutshell
You might say Import does not detect duplicate photos. So you have no way to point at various folders and be sure you imported that data. So I have no easy way to find out if my master catalog contains all my various drives (that I am sorting out) data.
I discovered this after doing a catalog import, I then did a standard import, not clicking import, pointing it at the photos folder of the catalog I just catalog imported, just to check if catalog import had worked. I selecting 'Don't import suspected duplicates', expecting to see zero or only a handful of orphaned files caused by incorrect deletion. It sees everything, every photo in the catalog!
The main things I tried which I think relevant to say...
- Since pointing it at the original /photos location on the other catalog drive did not work... I copied it to the same drive = no difference. (Some people talk about external drives causing issue, it ruled that out)
- Pointed it at its own /photos directory = no new photos detected
- Pointed it at its own /photos/folders I copied out to the desktop = new photos incorrectly detected.
- Create a new empty catalog and did a catalog import of the mothership catalog, repeat = same result in all cases of above tests.
- Try with one single folder of just 78 images = the same
- Tried on another laptop with the same version of Adobe to rule out virus, bug, software, laptop, etc... = no difference, it's not my kit.
History
I started with a detailed Community Forum Post: https://forums.adobe.com/thread/2443613 and then since I discovered Adobe don't bother checking those, I then moved to a support case. Then I was asked to close my Adobe Case Number ADB-928182-W8X1 and post it here as a bug. After spending about 3 days working on this problem the lovely people at Adobe really touched my heart by giving me a one month credit for the Photography plan. How totally touching, moving, rewarding, understanding of them. No bug (or do they call it an enhancement request these days) provided, I feel like posting it here is a just a place for customers to vent, nothing more.
I think catalog systems are a terrible way to design software. I like how Exposure uses single tiny files in the images folder, as it means multi-users can also work on the same data together. Maybe it's time to move off Lr.
Version
I am using most up to data Lr and stuff, Lr Classic CC 7.1