Ok - I've been experimenting and I may have solved this problem (at least for me)!
Background -
My MP3s were stored on the 2GB SanDisk card in 2 different ways ... Full CDs where I wanted all of the songs were in Folders by artist name and then inside those folders were folders by CD Title, which then held all of the songs.
I also had approx 60 individual songs that were not in folders, but were simply at the "root" level of the music folder on the microSD card.
Resolution -
What I noticed was that all of the songs in the music folder were showing in Media Player, but the Folders (by Artist/Album) were only available starting from "A" and down through letter "M". Every single folder where the artist name started after the letter "N" down to "W" were the ones missing!
As a test, I took all of the songs from 5 artists that were not showing, put those songs directly into the Music Folder @ root level and then deleted (from the microSD card) all of the Artist/Album folders. I probably moved about 20 songs and deleted 10 folders. BINGO
That must have freed-up enough slots in the Media Players file/folder list because now EVERYTHING is showing (and playing) ... even the many, many MP3s that are still in nested folders by Artist/Album. Very Weird, but all now seems to work.
/BD