Metadata!
After creating your comilation of files & tracks, then in metadata give them all the same album name-
Then use a metadata batch editor to modify the comlimation of tracks giving the tracks the same album name (I use the first part of car registration CU22) and numbering the tracks 1,2,3, 4……
If something is incomplete or corrupt, it will use xyz database stored on the headunits database. This could explain the car storing a file on your SD cards and USB sticks.