Yeah I was stoked to learn that DL Gold Medallion got me access to KLM lounges at AMS regardless of class.
Oddly, when I go to the KLM lounge web site and try to book a sleep cabin in the Non-Schengen lounge for my layover, when I enter my name and ticket number, I’m told “You don’t have lounge access with this ticket.”
It recognizes the ticket, and my entire outbound itinerary, on the KLM site, so I am not sure why it thinks I don’t have lounge access. Hopefully, it’s just a glitch that a phone call can address.