Just an FYI for anyone jumping off in Hong Kong. I am currently on my way to Danang. This is my second trip to Vietnam on these fares. At check-in, I was asked "Has this visa been used before?" (It had not). The agent then appeared to record the number of the visa. I did not notice this on my first trip where they just looked at the visa briefly. My point is just a warning to those who are getting off in Hong Kong to think twice before using an old visa because you know you are not entering Vietnam. I would be interested to know if anyone else has had the same experience.