Once tips and tricks get into the public, the loopholes tend to close quickly. Delta insiders don't post much on this forum, but they are constantly reading it.

One thing you want to double check is that KLM received the ticket number from Delta. If not, KLM might end up canceling your reservation for lack of ticket number. I know that has happened with other airlines/partnerships (especially Star Alliance), though I haven't heard it with SkyTeam. Still, if it were *my* reservation, I would contact KLM to double check that they show a ticket number in the reservation.