There's an urban legend about a group that did an unpublicized 24 hour distance event (so it's not 'published' on the interwebz), but the details were that a number of bikes were set up with calibrated odometers and GPS, ran on public roads and did just over 2400 miles. 2nd place only did 2388, or so the story goes.
The current official record is 2023 miles in 24 hours - done in South Africa. Iron Butt guys routinely do over 1000, but often have hyper-mile modifications like way oversize gas tanks, pee bottles and other niceties. For most, 500 miles is a LONG day.