Does anyone have a data point about trying to go to the Sky Club while on an AF/KL marketed, DL-operated Light flight with a DL Reserve / Amex Platinum / Membership? The last time I flew on a KL*/DL light itinerary, DL considered the DL-operated segments to be Main Cabin, although that was prior to the current Sky Club changes?
I know that VS uses T as the fare class for Economy Light and that on VS*/DL segments Delta treats that as basic.
It's possible system is just looking at fare classes, and not fare basis codes, for flights and will still let you in with a card/membership.