I played the expansion at bgg.con. There's suggested rules that you can use to make sure you get a new haunt from the expansion instead of one of the old ones. Also, do you have the first or second edition of the base game? If it's the second edition, then there aren't updates to the haunts are far as I know; it contains the already-updated versions.
*Edit* Just realized that you said 1st edition in your post. So yeah, there's a few tweaks to the haunts (and rules) that came with it. I dunno about the giant BGG document, but you can download the updated haunt books from Avalon Hill directly, along with the FAQ. I keep those in my Betrayal box.