Photoshop .abr files

[Doc_Pit]

I'm hoping someone can help me develop a better understanding of how PS 2021 handles .abr files.  The first image shows my brush menu.  Below that, the results of a system search for .abr files.  My impression was that PS could only access brushes in the ...Presets\Brushes folder.  However, other than General Brushes, none of the other brush sets available in PS appears in the Presets\Brushes or, for that matter, in the AppData..\... folder.  Of course, I do have these files stored on an external drive.  But they are nowhere on the OS drive.  Can anyone explain how PS is accessing these other brush sets?