On today's DL10 flight? That's not what I see. For D1 I see --
J5 C5 D5 I5 Z5 . Dummy booking is not particularly useful since lower fares will not be available for purchase this close in. From what I've seen, FCM offer is generally based on availability in the lower buckets and price does not have relationship with your original fare or booking class. Could be un-checking you in was not sufficient to return the offer.
Upgrades will not be available on delta.com or the Fly Delta app if:
- Any flight segment of your trip is departing the United Kingdom, France, India, Ghana or Honduras
- You have already checked in to your flight
- Any segment of your flight is operated by a partner airline
The UK and France exclusions are presumably because of the "luxury tax" which would require collecting additional money for premium cabin departures, although IIRC PS and D1 would have the same tax.
Partner segments make it difficult to calculate a price and then reissue the ticket.
Could it be that DL doesn't want to encourage people to call and un-check in so they won't make an offer if the person has already checked in?
BTW, this looks like odd fare class availability to me. I would interpret it as five empty D1 seats, but it's surprising that DL would be willing to sell all 5 at a Z fare or permit someone with a Z ticket to change to the flight (for example, after the outbound has been flown). If only DL would open more coach fare classes on the day of travel to make SDC easier when the flight clearly has empty seats.