Let me assure you - no wallpapers are missing. The ones you are talking about (11, 13, 14) simply got renamed due to being game specific (Abe's Exoddus or Abe's Odyssee) and not a part of the big 'series' pack. It's all now sorted out and all the files got proper descriptive names instead of just being numbered.
As for the artwork you like so much, it's now up for grabs as a wallpaper. You'll find it in the bonus section of Abe's Exoddus. Enjoy!