My "Zork Legacy Collection" CDs include PDFs with manuals, maps, and hints as part of the "Zork Anthology." This gets a bit messy:
The only manual included in the Legacy Collection is a (poor, B&W) version of the material GoG includes as "The Great Underground Empire." The rest of the manual isn't present. Maps included are (again, poor versions of) the Invisiclues maps from GoG's zip of maps. The "amazing map not sold in any gas station" isn't present.
Map is same as Invisiclues map from GoG's zip. Manual is (again, bad B&W) "G.U.E. on Nine Zorkminds A Day."
Manual's a lousy version of the "shareholder's report" although it includes the text which is blocked by the Festerton Town Library stamp. (I should probably get a scan of that....) Map's the usual invisiclues map.
So it looks like GoG's "shopping list" for content was the Zork Anthology as shipped, they just got better versions of everything.