If I'm not mistaken, Cherry resets their serials every year. So the 5000 would be the first one produced in 1998, and the 3484 the first one produced in 2006.
Cherry G80-3484HKCUS were not that rare as far as I remember. I mean they were more expensive yes, but you could purchase it in S.Korea no problems. I wasn't interested in full layouts so I didn't bother but this was a few years ago so may be they're hard to get now.