DL does not offer comp upgrades to D1 on international routes. It doesn't matter how you book the flight.




Once you have selected an online seat upgrade offer, you will not be able to further upgrade the flight (other than perhaps reversing original upgrade for an eCredit as they are non-refundable). Again, this does not depend on how you book the flight and will also be the case when booking flights on delta.com.

The DL online seat upgrade offers are only offered on Delta flown and Delta coded flights. When you book flights with miles, they are always coded with the operating carrier (and thus eligible for online seat upgrade offers on DL flights). When you book revenue flights, they will generally be coded as the carrier you are purchasing the flight from (a VS coded, DL operated revenue flight would not be eligible for the DL online seat upgrade offers).