What is the relationship between the .lib files?

[paulvdh]

For the cache file:

What are the cache and rescue libs and how does the schematic rescue dialog work? (KiCad version 5.x and earlier)

The purpose of the cache library KiCad version 5 and earlier do not include symbol information in the schematic file format. Without any counter measure changes to the libs would change the schematic without user control (worst case a symbol is deleted from the lib and the project looses its information). This is where the cache lib comes in. Anytime a user adds a symbol to the project it is copied to the cache lib for save keeping (unless the same symbol is already in the cache). If now the li…

Apparently you have made a new library in your project.

@AndreKR

I don’t have (and don’t need) a sym-lib-table in the project.

Euhm, no.
If you want to use that library in your project, you have to add the library to your project, and KiCad saves that setting in the sym-lib-table file. Result is that if you delete the sym-lib-table file from your project, then KiCad does not see the project specific libraries anymore.

Library management in KiCad version 5

Disclaimer: screenshots taken in nightly from between version 5.0 and 5.1. Version 5.0.x looks slightly different. Version 5.1.x will look like the screenshots show. This is a detailed lecture. If you want to know how to simply add some assets you downloaded to KiCad then you can read the shorter tutorial How to get a downloaded symbol, footprint or full library into KiCad version 5? Summary KiCad does not automatically detect libraries! There is no special library location (you might still ca…