Where do we get information for the database?

Forgive me if this is a silly question.

Every expansion changes the stats of items and mobs, changes talents, spells, abilities, etc. etc. etc. When we create a server like Trinity we have to find this information to put in the database.

But where do we get this information for previous expansions from? Websites like WoWHead are always updated to the current expansion, so the information displayed on sites like that wouldn’t be correct for a previous expansion like Wrath. Where can we find this information? I know of sites like classicdb.ch but are they complete? And as far as I can tell there’s no way to download all of the information in their databases.

for WoTLK - dbwotlk.com