No BTM folder in my unit (either 3790 or 37xx->34xx). Maybe Region dependant or more likely, mobile phone model dependant. I don't get phonebook either on my device (have 'older' LG phone) which may explain missing files.

006B121102.GCD (Touchpanel software version 1.23) This file has differences to the 006B121102.GCD posted for 37xx on other thread. Compared files in HexEdit. Maybe filed is 'tuned' to give accurancy on different production runs but seems silly if Garmin giving different files the same name.

Suspect \Audible is created only when loading an audio book.

006B139900.GCD could be the interesting one for HD receivers maybe?