Hi Scott,
Did there happen to be a drawing with welding symbols indicating how the joint was to be welded out?
If so, the symbol itself would/should have indicated if the joint was a fillet weld, a partial penetration weld, or a full penetration weld.
Just because it was to welded in accordance with D1.6 doesn't tell the welder how to weld the joint, and more expecit instructions(drawings with welding symbols typically) should be provided before the joint can be properly welded. Without drawings or welding symbols, there is no way to know which WPS(welding procedure) to use to be in accordance with D1.6.
EDIT...I read too quickly, you did mention drawings. Can you show us the welding symbol on the drawing? The symbol is the clue to your puzzle.