https://www.gamespot.com/articles/world-of-warcraft-classic-gets-new-details/1100-6459909/

World of Warcraft Classic is coming; we may not know exactly when, but we are getting a better idea of some of the challenges and achievements of the developers trying to make it happen. In a "Dev Watercooler" blog post, Blizzard revealed more details about the prototyping of the game, and reassured excited fans that the re-creation would do the vanilla version of the game justice.

"The process of restoring the classic game is not straightforward, and it's important to us to take the time and effort to get it right--this includes [pouring] over numerous game versions, data, and code; meticulously scrutinizing all the changes we've made over the years," Blizzard's dev team wrote.