sadly I have first hand experience of this although it wasn't a race but did indeed get overlooked by the sweepers and NO I WAS NOT SHOPPING
Fair point that though in many races where the routes are so varied it would be a difficult job indeed although I have acted as sweeper a couple of times on 'fixed' routes it was a good day out yes but the main job wasn't to shepherd all the runners but to collect the tape and markers that had been previously laid out