Special Edition pieces were created to add an extra incentive to buy a boxed set. They were also used to promote the Warhammer and 40k game boxes for Christmas 1999. A series of Army Standard Bearers and other items were then released in the new Army boxes from 2000 until 2007. After that the army / battalion box contents became all plastic models and special editions were discontinued, until the Warhammer 40,000 Dark Vengeance set was released in 2012. I have stopped tracking the Army Box Special Miniatures after that point as their status is oftern ambiguous.
Some of these were also available through the Skulz program.