I have tons of CDs and other files (bootlegs, music made by friends etc.) from USB sticks that I have slowly been importing in to Music.app for the last couple of weeks, and I'm just confused because I was only expecting to be able play those songs from the Mac I'd imported them on to. The majority of them are not available for sale in iTunes, and therefore would not normally be available via iTunes Match (I have an Apple Music subscription). Yet I am able to download the imported tracks to my iPhone and other devices. I'm not complaining, but I can't find any information about this anywhere. Tl;dr, I thought Apple Music tracks only synced across devices when those tracks were available in iTunes?