Well this is interesting, I just booked a multi city LHR-JFK-JAX; ATL-CDG-LHR through Delta for 4 weeks from now. LHR-JFK is VS metal, ATL-CDG-LHR is AF metal, opted for the CDG layover since it was $600 cheaper than a nonstop ATL-LHR flight. I booked premium economy for all legs. This is an interesting one though, so I found this itinerary on Google Flights and booked through Delta. For some reason though, the LHR-JFK-JAX was all DL coded, but somehow the ATL-CDG-LHR is VS coded. I booked through DL (and ticket shows 006 stock), yet half of my segments are on AF metal, and those segments are VS coded. Never seen anything like this before. I call DL though to apply a GUC to the AF legs since according to ExpertFlyer there is space for a GUC business class upgrade. Well, there is indeed space, but they can't apply it since it's somehow VS coded. I'd really like to use a GUC on this since it's an overnight flight but I've never seen anything like this before. The Diamond agent and global ticketing department had also never seen anything like this either. Any suggestions on how to handle this?