Perma-Bans seem to be that you have screwed up so badly that the Moderators do not want you around.
Every once in a while, Hell freezes over and a perp is able to walk back across the ice.
ie> DenniFloss, Dug777, etc
And then with the new changes; people were re-evaluated based on the past transgressions to see if under the new guidelines, they would have been allowed to stay.
Those that met those guidelines and were able to admit that they had been in the wrong, were apparently allowed a second chance to show that they could be redeemed.