You are right of course and many events follow this course. Same policy at Lifeline (though inevitably at a nine hour event one or two slipped through the net while DJs are outside having a fag or summat) but generally NO repeats. Same thing at Essence Saturday night - which is a toughie if you're on last like me You sit there listening to all these gems getting dropped in ahead of you. Same thing at the Herts and Beds venues such as the Irish Centre, Blue Skies, Spirella, and The Ath, where the DJ's agree not to re-programme sounds that have already been played that evening. It's easy really and it's not an uncommon approach.
I accept the point about turning up early, but not always possible on a Friday evening do.....I physically cannot get to a venue much before 8 30 and I think if something is played early doors it may be OK to spin it once again later when the place is heaving. But there in heart and spirit and agree with the non repetition spirit.
Steve