What awesome work! I see that even more artworks have been added over the past couple of days.
I do see a few issues with the artwork that I wanted to point out. No biggies, just wanted to see if they could be fixed with the layouts:
For example Squish: When you switch to Screen 0/1 Pixel, Dual Over Under / Gapless, Screen 0/1 standard, the overlays are not being shown. Can you add the overlays to these configurations? Then you can turn off the overlays using the separate toggles in MAME.
When you turn off the bezel, you can still see a white outline of the bezel on the screen.
For SMB: I really like the animated button presses, but they only work on the new wide screen artwork.