maybe cos the roms that u have r named by the Gbarenamer Dat. OffLine list uses the skybaby dat for renaming the roms. I have the same problem and on 500 roms the offline list found only 181!
LOL
If you want that offline displays the boxart instead of the main screen of the game, pick the game u want to display,look at the number (if is 0859,u have to create a pic named 859a.png),resize and save the boxart as a png whit the gba displaysize (for this operation,use AcdSee),rename it as the release number,and put it in the right images folder. that's it.