Originally Posted by
javabytes
So if you book Delta-marketed flights, you can book any fare class except E, and upgrade into KLM Z class. If you book KLM marketed tickets, you need Y/B/M.
That's really good to know. I have been given the answer the OP got and took it for what it was without pushing it. Would be interested to hear how one goes about convincing a DL agent to push for KL Z space on a DL coded. Specifically, what was said and to whom.