This art book covers LoS, MoF, and LoS2.
https://twitter.com/CastlevaniaLOS/status/393454216296931328
LoS2 LE art book covers only LoS2.
I make it a point to play it safe when it comes to Cox: no matter how many compendiums and complete editions he releases, you can always expect for an even more "ultimate" compilation to be lurking somewhere around the corner.
I'll be buying the "Super-mega-ultimate everything LoS Castlevania" anthology when it comes out, but I don't expect it to be released before a good year or two. So, until then, I'll wait, and hold off on the half-collections and almost-there editions -- the last thing I want is an unpleasant surprise.
That said, I'd be the first interested in a definitive LoS art compendium; I'll have to admit MS's art design isn't all that bad. I just have to make sure that I choose the right one.