I had this problem at AMS last year, boarding DL's AMS-SEA staffed by KL ground staff. I don't remember what my boarding pass said. I had brought my AS MVPG card just in case, but unfortunately, I had grabbed my prior year's card out of my drawer of cards.

They were fairly unhappy with allowing an AS MVPG to begin with and became more so when I showed them the expired Gold card, but I politely insisted, and they ultimately let me through the Sky Priority lane vs. sending me back to the end of the regular line. I think they confirmed my current MVPG status in the reservation.

I feel like I have gotten Sky Priority treatment when I have had my current MVPG card, and/or my boarding pass has said so, even from KL and AF stations.