Don't know much about "competition" records, but the longest recorded combat knife kill was by George "Skeeter" Vaughan, a Cherokee (Cherokee name "Gray Otter") from Tennessee.
He took out a German bunker sentry with a modified bayonet at night. He got as close as he could without being spotted - the intervening area had been cleared of brush and was covered with snow - and, as he later put it, with a lot of luck, hit the sentry in the neck, killing him instantly. Any attempt to get closer would have been spotted, allowing a warning to be passed to the bunkers.
The throw was measured the next day as being from 87 feet. The silent removal of the sentry allowed his unit to quickly roll up a line of machine gun and artillery bunkers, saving countless lives during the next day's assault.
So for me, any other "record" is fluff.