ok, I know of Ark volume 1 (USA cartoon), Ark volume 2 (Japan), Complete Ark Compendium (USA/Japan) but I keep reading about this Ark Addendum. Please help!
That was series of posts on the author's blog, showcasing things that there wasn't room for in the book, or that he obtained after its publication, that's all. Mostly backgrounds, props, and transformation sequences.
Also, Jim Sorensen is awesome, you should follow him on Facebook/Twitter and ask him questions! But not too many as that is generally considered to drive people crazy.