A:Answer Hello ebizzle - I found the below information from a site that did a review on the Part Box "On The Go" model. I am guessing the PB300 may be the same folder read and playback (?)
https://techaeris.com/2021/05/03/jbl-partybox-on-the-go-review-a-fun-and-excellent-outdoor-portable-party-speaker/
-The JBL PartyBox On-The-Go supports up to 8 subfolders.
-Playback will occur in alphabetical order with main folders first, then subfolders.
-Use the controls at the top to skip songs, play, pause.