In 10 years on the console, I heard 4 Mayday calls, one on area, the other three on HF (it was a Designated Remote Area). All were answered either by me or another ground station. One of the HF ones was a relay (maybe), and was from another pilot who witnessed the crash, (the victim had no time to transmit, we had VHF in the CCT there and he said nothing on VHF while airborne). It would be interesting to know how many are actually relayed in by other aircraft, be they high flyers hearing something on 121.5, or otherwise. This whole argument may in fact be pointless.