Looking at booking Delta operated flights through AF or KL on 057/074 ticket stock. Can a GUC be applied to a Delta operated flight marketed by AF/KL with an AF/KL flight number?
Yes, any Delta-operated flight. From
https://www.delta.com/us/en/skymiles...llion-upgrades
"
Upgrade Certificates can be used on any Delta-operated flight, and select partner-operated flights with KLM, Air France, Virgin Atlantic, Korean Air and Aeromexico."