Originally Posted by
ATOBTTR
There's actually an 11th Boarding Zone: Military. which comes after the first group of pre-boards and usually before Delta One/First Class.
And possibly even a 12th boarding zone...those who volunteer their seats for a VDB voucher and at the very last second before the doors are closed are told to board as DL ultimately won’t need your seats after all due to no-shows who checked-in or confirmed passengers stuck in Customs or on a tight connection.