You found the correct place for Trail Crest exit permits. They are made available exactly 6 months before you hike... only they open it for 6 more days within the 6-months if you are getting a permit to start on another trail.
The permits held back for walk-ins may possibly be gobbled up by hikers coming in from a farther distance (and more days), since they will be trying for the exit permits when they pick up their entry permit.
