Indeed... there are a few artworks that have a serious problem regarding the spacing. I don't know the correct terminology, but if you play the game with the artwork you uploaded, you'll see that the character you control and the enemies get hidden around the borders. For instance, in gaunt2.zip, if you move your character to the top of the screen, he'll disappear behind the bezel because the spacing is all messed up. You'll see what I mean when you play the game with the artwork...
Well, here are the games that have this spacing issue:
centiped commando digdug gaunt2
Also, the defender.zip does not work. The bezels don't get displayed.
And one last thing... for gberet.zip, you forgot to include the original artwork in the zip.