i think we already got a similar topic about the same issue..
as DIO said, at first calling something a "Mix" was due mainly to describ different versions produced by the same DJ.. like an "Extended Mix", "Vocal Mix" and things like that.. whereas when someone goes on the remix the track is called by a "Remix"
now with many different mix names like AvB's "Rising Star Mix" remixers started to call their remixes as "Mix" instead of "Remix"..
nowadays there's no actual difference, though still the different version of the same track are called "Mix" and not "Remix" but it doesnt work vice versa anymore!