Check my post
here. Maybe it will shed some light on using the USB and organizing files.
Further, I use
this app to ensure that everything displays in alpha order.
I think I have way over 200 song files - never bothered to check. I've yet to not find a song on the USB.
Overall, I am surprised that the FRS does not have more current file management capabilities. I dislike having to rename every folder with the name of the Artist just so the display/selection makes sense and is usable.