ikantspelwurdz: Ok.... let me see if I understand this right.
In 1992, NWC released "normal MM4" on CD-ROM, but didn't include full voice, so very little of the CD-ROM's capacity was actually used.
In 1993, NWC released "normal MM5" on CD-ROM, and likewise didn't have full voice, and didn't use much of the capacity.
In 1994, NWC released "World of Xeen," a 2-disc game that included all of the content of the previously released "normal MM4" and "normal MM5," plus full voice acting that filled the capacity of both discs.
And what's included here is not "World of Xeen," just the CD-ROM versions of "normal MM4" and "normal MM5."
Is that how it goes? Or is there a "normal World of Xeen" that only has partial voice and was released before 1994?
Right, almost.
If you install MM5 over MM4 you get World of Xeen. GOG's version is already combined (MM4&MM5). And yes, originally MM4 & MM5 were released on floppies only, I was not sure about that. So GOG's World of Xeen is the combined MM4 & MM5 floppies version.
Here's a (rather old) list of released Might & Magic products, but shows what you want to know: