Engine Library on USB stick and internal HD

I just got my Prime 4. Previously used Serato. I have all my music on external USB flash drive. I have imported all my Serato crates and tracks into Engine Prime, and have created a number of playlists in Engine Prime which contain tracklists of prepared mixes. When I plug the USB into Prime 4, only the crates appear ie none of the playlists are visible.

There is an Engine Library folder on both internal HD and USB, the one on internal HD has a lot more files in it. I assume these files are what tells EP what crates I have and what tracks are in there? If I load EP without the USB plugged in, I can see my playlists. So it seems to me the library folder on USB is missing some of the data relating to my playlists. I guess I can copy it over, but does anyone know how i can make sure the Library folder on USB replicates automatically the same folder on internal HD?

thanks