I call this myth busted because I looked at my passport 10 seconds ago. There is no exit stamp last time I left on a tourist visa. No stamp from Hong Kong because they don't do that any more. All there is to see is the last renewal stamp and then a re-entry stamp. Which is what I am saying this may be what the yachties do. They just go to BI and say they were out sailing to (pick a place that does not stamp visa) and they are back now and reporting in.