In case anyone is interested, as I can see, when you install a Kontakt library this happens:

An entry with the library name is written in
HKEY_LOCAL_MACHINE\SOFTWARE\Native Instruments
CURRENT_USER\SOFTWARE\Native Instruments

It checks if it exists in
C:\Program Files\Common Files\Native Instruments\Service Center\NativeAccess.xml
This is the database of all NI products, including the official Kontakt Player libraries

A json file with the library name is created in
C:\Users\Public\Documents\Native Instruments\installed_products
*This is new in Kontakt 8

If it is a custom, unofficial library (not in NativeAccess.xml), it creates an xml file with the library name in
C:\Program Files\Common Files\Native Instruments\Service Center

As for the thumbnails, they are taken from
C:\Users\Public\Documents\NI Resources\image
and from
C:\Program Files\Common Files\Native Instruments\Kontakt 8\PAResources\image
indistinctly.

As for the way libraries appear within Kontakt, it's not all clear. In previous versions, both in the classic rack view and in the new browser, libraries appear with their name (which appears in the <name> field of their nicnt and in NativeAccess.xml). However, in version 8 they seem to appear with the name of their developer first, for example, 8Dio Majestica Professional.
However, as always with Native Instruments, there are inconsistencies. Berlin Strings from Orchestral Tools, following the new standard, appears as "Orchestral Tools Berlin Strings", and the same goes for Brass and Woodwinds, however it appears as "Berlin Percussion" instead of "Orchestral Tools Berlin Percussion", as you would expect.
I believe it is impossible to correct this inconsistency. It does not exist in any text file or database on the entire computer with the name "Orchestral Tools Berlin Strings". The only thing that exists is "Berlin Strings". That is, it seems that the name "Orchestral Tools Berlin Strings" simply exists in the Kontakt interface, not taken from any text file or database. Strange, at least for me, who am not a programmer. If anyone knows the explanation for this mystery I would appreciate it if you could explain it.

 

don't use that fucking special caracters [ ] in the library folder name

Majestica Professional-[8Dio] is bullshit
Majestica Professional only is good

only the public folder images will be loaded, idem for maschine and komplete kontrol.

generally, kontakt scan the program common files PAResources to finalise the database and export the thumbnails (when installed from setup) in the public folder.

but it is not allways the case, or done with extracted libraries. it need to extract them from the nicnt file.

check regedit & json ContentDir location in case something is missing, badlly scaned without location.
use total commander to extract the PAResources if missing.