The cabin is identified by the second to last letter in the fare basis code. If it's a "D", it's a D1 fare -- end of story. DL doesn't play coach with instant upgrade games (that's an AA thing). The X at the beginning of fare basis code just means there's a dual inventory check. Most domestic FC fares are like this and no one has reported issues with getting credit for those. There are also domestic D1 fares with dual inventory check. I'm not finding any international fares right now (it would be helpful if you could tell us exactly what you are looking at), but I doubt you will have issues.