There's other stuff on Amazon (usually gathered by the people from masterworks forum in one handy thread), for example Deadpool Classic vol. 12: Deadpool Corps, which would confirm that vol. 11 is Gischler's Merc With a Mouth. Well, it was obvious from the subtitle, but not everybody believed it. I personally think this is weird branding, because those two books would make more sense to be put out as Deadpool by Gischler Complete Collection or whatever.
Is there somewhere a definition of omnibus that says 'has to have X pages'?