This depends on your definition of accurate in terms if privates.
Private servers got their info not from a 1.12 server, but various guides, videos and memories of playing the game - most of which wasn’t 1.12.
1.12 was the final patch meant to catch everyone up quickly before TBC. Dungeons nerfed, damage/regen rates retuned, etc.
Not to a great degree, but enough of a change that many who did play Vanilla for MOST of its life won’t remember what 1.12 actually felt like.