Originally Posted by
therealstegblob
It was indeed a retcon. Sargeras' original, original lore was that he was corrupted by demons (specifically the Eredar), this was changed around the time TBC was being written (as you mentioned) to Sargeras corrupting the Eredar, because Sargeras had come to believe all life needed to be destroyed in order to stop corruption.
However, the lore has now been tweaked further and Sargeras wants to reset evolution in the universe, not destroy it completely. The lore also crowbarred in Void Lords, expanding on Sargeras' already established canon. It's a retcon. I write fiction for a living, my man, I know what a retcon to established story is.
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Refer to my above post, but the inclusion of the Void Lords is indeed a retcon. The Void Lords were not revealed to be the "true bad guys" or whatever, they were added to be the true bad guys. There was no pre-existing build up or even slightest suggestions that the Void Lords existed, nor did the story organically add them on its own (i.e., characters realizing the Old Gods were created by a 'greater force' or something), they were artificially added into the lore with no build up or story vehicle of any sort in the existing canon; this is what a retcon is.
Though adding a new character is technically not exactly a retcon (though the two things can go hand in hand in certain instances), the inclusion of the Void Lords is part of the retconning of Sargeras (again, refer to my above text).