Interesting question: About a year ago I was minding my business having some lunch at the CX The Wing First Class Lounge and there was a gentleman next to my table who had pulled out his passport to look at. The passport was incredibly thick, it must have been as thick as a ipod. I made some chatter to him and I said there must be at least 8 additions to that passport. He laughs, replies no, there's 15. That's right FIFTEEN! He even let me count through the additions. It was a mess of visas, it was probably nearing 1,000 stamps.

Come to know, this gentleman was based in Taipei and his company had transferred him to Hong Kong, but since he had some children and had already settled down in Taiwan, he took it upon himself to commute each week for the past 3 yrs.

So, the number is at least 15 additions.