West Coast,
ALTRV's must still be approved by the appropriate FAA Facility, so again if the block altitudes are NOT available, then the requested block doesn't get approved.
What you may be thinking is back to the days of when SAC use to flush all their aircraft out during an alert. Huge blocks of airspace would be blocked to allow SAC to depart, and climb out. I haven't seen a flush in a very long time.
Mike