Originally Posted by
woodenshoe101
Are you looking on DL.com for the GOT-AMS segment only? If you search for it as a standalone intra-EU flight it will not show up on DL's site (it will tell you that DL does not operate flights between those cities). This is true even if the actual flight is a DL codeshare - the codeshare is only visible and can only be booked if combined with a TATL segment. If you search GOT-AMS-US, it should show up on DL.com if still a valid flight.
OP needs to be careful here. If the agent rebooks the entire ticket GOT-AMS-USA, this could cancel the GUC upgrade. DL in principle could force it, but I'm not sure they would easily be willing to do so if upgrade inventory isn't available.
I'm not sure whether OP is upgraded into EuroBusiness on GOT-AMS or even cares.