I just took the class yesterday in Jefferson City, MO
Mike Lake was our instructor and he said that a database is in the works at KCBS headquarters for tracking CBJs This was apparently instituted because a lot of judges are no-shows at contests where they've offered to judge.
At some point before the competition, the organizers, reps and headquarters are all going to make sure the judges signed up are people who actually show up.
ALSO - in the red covered book I received as part of the class, there's a page at the back to document all of the contests I judge at. It says right at the top that a judge who is unknown to the contest officials may need to produce identification. This sounds like to me that, if I have a CBJ card with a number on it, that I may still need to produce some supporting documentation that I am who I say I am before I can be allowed to judge.
In the book it also states very clearly and in bold type at the top of the Instructions for Judges page that "You must maintain your KCBS membership to keep your CBJ status".
I believe that, in most cases, CBJ's are scheduled and verified ahead of the competition. The only time this might present a problem is if an organizer needs judges at the last minute because of no-shows and presses someone into service.
From what I learned yesterday, the KCBS has this potential problem covered.
But that's just my two cents . . .
P.S. Competitors are NOT required to be KCBS members in order to compete. That exact question was asked yesterday at the class.