It's simply that when you start to enumerate who your passengers are, such as stowaways, trespassers, or any other person who doesn't have permission or who is not coming on board with the knowledge of the shipowner or operator, you're including even officials of the local port, customs and excise, and so on. So in the interests of clarity, you either leave it out or you start to enumerate them all.
On May 5th, 2009. See this statement in context.