iTunes Playlist & USB

I've searched every where and couldn't find a solution to my issue.

I have a iTunes playlist with 250+ songs and when I created the playlist I'd exported the playlist to my 16GB USB to use in my car that has an intellilink radio system. The playlist worked fine and all songs were playable.

Now this is where things go real bad!

Whenever I add new songs to the playlist and export the playlist to the same USB, the new songs will show, but NONE of the original song tracks are showing when I use it it my car intellilink radio system. All songs show when I play the playlist on my computer with the USB plugged in.

If I create an entirely new playlist with the original songs and the new songs which I've done once before and it took me several hours to do all songs will show and play in my car using the same USB. If I add new songs to this new playlist ONLY the new songs will be available using the USB in my car.

Any ideas?