Late to the party but I agree
I have been adding booklets for a while and never noticed any MIA , but I do rename everything to a bald “booklet.pdf”, even lower case . In the same way I always name the primary cover art file as “folder.jpg”
As @Mark_Sealey says these files go in the main album folder, this works …(for me, this is an internal SSD in a 10i7 NUC/ROCK)
