#error!angel

Angel doesn't really exist in most AU's. The reality is that her universe is separate from all others, a divergence that occurred semi-naturally. The Underground is empty in the base of Angel's AU and Resets don't work, not to mention it's difficult for Outcodes to get into the AU in the first place. Monsters that were driven Underground died off for some reason, which causes Angel's AU to attempt to correct itself by colliding with other Universes.

Because of this, her AU has a nasty habit of yoinking copies of the Underground from other universes. Every time Angel dies her AU splinters off, causing a violent reboot to the moment the barrier is broken in an attempt to keep itself going. The nature of the AU means that it's impossible to tell what other universe it might snatch the monsters from.