Wow. Good luck. What DL needed to do was to print paper tickets for you. That is what FLT COUPON REQ means. I am not sure that "Delta didn't pay for it." They just didn't go through all the proper steps.

What you need to do is check with Korean to see if the flight coupons are unused or "open." If so, that might be your recourse. Checking directly with the DL agents at SMF is a good start. Hopefully someone there will recall the situation.

My guess is that with Korean in the mix as well, you will have a really hard time getting this settled.