Suspect the calculator is wrong and it's 3x for Plats in PS and 2x for non-status passengers in PS. FWIW, the DL Amex card is not a +1 luggage benefit (other than for Silver Medallions domestically) and has no bearing on flights where you already get at least 1 bag free. As already noted, there's no way to add, combine, or merge separate reservations. They can only be "linked" which doesn't really confer any benefits. It's only a notation on the reservations largely there to assist agents in keeping pax together when there are schedule changes.