Originally Posted by virtualtroy
Although I've got two D class seats booked on this flight under the LA designator, I'd prefer to use the QF designator because of mileage bonuses. However, D class availability has for the QF flight # has been at a steady nil ever since booking a few months back.
It is quite possible that QF is not intending to offer any D on their codeshare flight number. Since most D is for RTW type multi-carrier fares (not all, but certainly a lot of it), QF may not make enough money out of selling D seats on their codeshare service to warrant it. So they may just leave the D up to LAN for those services.
For example, QF has to buy the seats from LAN in order to sell them as their codeshare flight number. The total cost of a DONE4 is $9169 less any discounts/commissions offered. So if we assume a DONE4 incremental revenue to QF on a D sector of a DONE4 is likely to be something in the order of $1000 for an inter-continental sector. They can sell a J seat for more like $4000. So they may well lose money by gaining the $1000 for your D seat, paying LAN whatever is owed as part of the codeshare agreement, and also paying you out the FF points.