Uh, I don't think so Tim...
Yes, a table captain you could figure out the "add to" number but no judge sitting at the table could come up with the magic number.
The only way to know whos box is whos is to know the teams box number and then the "add to" number. I think a judge at a table would have no way to complete this task.
The double blind is safe and secure.
Ed
KCBS does not use a true double blind system. It's a blind system. It's unlikely that a table captain or judge would ever learn the alternate # prior to judging, that's true. But the fact is that the system is not double blind. There will be a handful of people that have access to that info prior to judging.
IBCA is an example of a double blind system. The box given to a team has two tickets with matching numbers attached. The team retains one and the other remains on the box. The judges, head judge, volunteers have NO list to determine which team was given a particular #. That is a double blind system.
Either way, I think this has diverged from the original topic.