How is the "Accumulated Bullion Discount" different from regular volume discounts?

A traditional volume discount applies to a single product type in a single transaction, hence only large orders enjoy volume discounts. Silver Bullion's accumulated bullion discount applies across product types across your transactions. This is true regardless of order type, so you can keep accumulating boz regardless if you are storing through S.T.A.R. Storage or buying and taking delivery of your bullion.