I don't understand how they are able to replicate all the interaction rules. There's a bunch of things going on in WoW, and unless you did a heck of a lot of experiments how would you uncover the rules governing all the interactions between different things? For instance you can bubble hearth on classic but not in hardcore. How is an external server developer going to know that?

Also how do they place all the NPCs and hook up the quests and lot tables? Do they scrape wowhead?