WoW is MMORPG, KB is a simple SP game. If any MMORPG forces incompatible saves, it will be the end of it.
I can think of a number of games that had incompatible saves. let's take the Heroes series, for example, as this game resembles them a bit. You couldn't take a heroes 3 game and turn in into armageddon's blade with the new content - you had to play it as it is.
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