The release of Classic has caused a lot of arguments about how much damage mobs did back in the day. Most people agree that Classic is accurate as to patch 1.12, the final patch in vanilla, but there is a lot of disagreement about what changed between 1.12 and earlier patches.
What is fascinating to me is the lack of hard evidence. People point to blurry vanilla era videos. Apparently of the probably hundreds of thousands of people who fought Ragnaros back in the day, none of them saved a combat log. Not even Blizz has a backup.