Technically, if someone wanted to make a fuss, I think you're supposed to use the SC as a member only when you are flying (on any carrier) that day, presumably from the airport where the SC is located. So even if you got the gate pass and were able to get through security without buying a refundable ticket, you might have had to do this to sue the SC.

Is RDU a small enough airport that the "never ask again" really matters? What would be the chance of getting the same agent who would remember you? Not that you're not memorable or anything....

The opposite of no one time exceptions is no waivers/no favors, which I think we all would hate. Sometimes the "one time only" sounds a lot like the school teacher who threatens to put something on your permanent record. I'm not at all convinced that airlines actually document this stuff, although from what I've heard, other carriers might be more likely than DL to note it.