Will my folders work better if I use a microSD card?

Here’s another thing that makes absolutely no sense to me.

I bought a box set of Bob Marley and ripped all the music to one folder on my computer (all songs discs and songs were ripped in the exact same manner).

I then created four folders in the exact same way and put mp3 files into each folder to make playlists.

I copied all folders to the Sansa, but only one folder is visible under Music >> Folders.

How can this happen when all mp3’s, and all folders, were created in the exact same manner?

Shouldn’t either all folders not be seen (or all be seen) when I go to Music >> Folders considering all were created in the same way?

All ID3 tags, or lack thereof, are the same for everything, so please explain how some can be visible and some are not.

Thanks,

Jeff