Mystery Member of the Garuntee Group

I've always known there to be 9 members of the Garuntee Group. However, I came across a tenth member, Joey Thompson on ET's list of those who boarded Titanic at Belfast. But, on his biography, it is said he disembarked at Southampton. Why is he a Garuntee Group member, then? And, if he is, then how do you explain the ten members? Did Thomas Andrews not count as a member?
Thompson bio:Mr Joey Thompson - Titanic Passenger
I'm new and also very confused. Please clear this up for me.
Joey Thompson was not needed on the maiden voyage. He made the voyage from Belfast to Southampton as a painter, doing with his stuff the last work on the ship.
Including Thomas Andrews we have 9 members (without him 8) of the Guarantee Group. I guess it depends on how someone count them. I think in many books you will find that they were 8 members working under Andrews.