Well I don't have one parked in front of me, but those Daytona models were an attempt to differenciate the luxury Cordoba from the "sporty" Charger using stripe tape and paint. I highly doubt the tooling dollars would be spent for unique doors on a sub-model.
More likely, the tape/paint job was done in the studio. Somebody liked it enough to make it into a tooling change when the budget was available in '78. Liked it so much they even changed the name to Magnum.