What are those 19 by any chance? There are quite a few that are only for diving, e.g. Cocos, Aldabra, Revillagigedo Islands, I suppose Bikini Atoll as well. Charting a boat/flight just for the tick might be possible if you got the money to burn. Maybe he is a diver but the demo doesn't fit. Plus there is Wrangel Island, I suppose we count Surtsey with a boat-trip, Gough and the INACCESSIBLE islands, the French Austral Lands that take 30 days by boat or whatever. I think there are 30+ that even us die-hard traveler would have serious issues with, SGang Gwaay is pretty much canoe-only. Now this is all without mentioning that the person is a Chinese national and they have limited visa access to many countries, e.g. PNG takes 3 months to get a tourist visa which would be a huge issue unless he's got a second passport. Lastly he's keeping up with TWHS the entire time so get all of last years addition so quickly, especially off-the-beaten track like Coal Mining Heritage of Sawahlunto? I don't think so or at least he would maybe come visit here and say hi, right? If so I'd be very impressed and would like to hear about travel tips to those hard-to-reach places.