The devil is in the details. "Once in a while" is an impossible policy for a corporation with hundreds of front line agents. Give agents the power to waiver the rules, and they will waive them. If the restrictions on cheaper fares are not enforced, people will always buy the cheaper fare. The extra cost of a few pints in the lounge is insignificant compared to the lost revenues from passengers buying cheaper fares when the would otherwise buy more expensive fares.