Another important question is: "what are the consequences for a gold member, who doesn't adhere to the light fare's rules (yet hasn't checked any bags)"?
So let's say they do notice at the gate, that you are carrying one piece of luggage too many for your on-board allowance. Then what? The rules dictate, that your bigger bag will be checked and sent to the cargo hold.
In most cases this will come at a certain cost, however you are entitled to one piece of luggage up to 23kg as a gold member (which you haven't made use of), so on what grounds would they then charge you? Or wouldn't they?