A different flavor of discount is the two 50% off beer/wine. On sea days I may want to use that for a beer by the pool and save my D+ vouchers for a mixed drink. Just let the bartender know which discount you want to use because as others have noted the bartenders will default to the diamond vouchers.
Just off Alure yesterday & they were not delivered. Saw a few pax around the ship reading them so perhaps they know the black-market section of the ship to obtain them.