I've seen someone waved the Gold card at the J Lounge and muttered that he was on J seat and decided to keep walking. Despite the queue at the counter, the lounge lady summoned the person back and made him wait, then scan his card to ensure he was indeed on J before allowing him in. I thought that was fair. Personally, I have stopped for breakfast after the red-eye flights into MEL and there were no problems (so far anyway).