How are Vanilla Servers made?

[poku]

I've always wondered and googled several times.

Where is the information about vanilla wow found that the devs use to make vanilla servers?
Specific loot drops, monster spawn locations, pathing, loots, stats, skills, just all that information required.

Is it reverse engineered somehow?

[Guirssane]

archive, database, patchnotes, etc etc

[mrmr]

http://archive.org/web/
Old books and guide.
Bestiary.