Went ahead and book on KLM. Called Delta to request economy comfort seating and next time when I logged in to see my booking, what would you believe, we were all sitting in EC. I was not even prompted for any payments, so I thought it's all kosher. But yesterday when I logged back, we were back to unassigned seating and selection of any premium seating prompted the standard payments, not even any discount for me as a DM. What could be going on? Could anybody shed some light with their similar experiences? I ended up booking directly with KLM.