Norm has brought up a good point, if the problem came after the first few were struck the NON ERROR will be the tuff one to find. From what I have seen on the error and what Jay points out about the letters being part of the word Blackjack I would say it is what coin collectors call a die clash which is caused when the two dies hit each other because there was no blank inseted in between the dies when it went through the strikeing cycle, if IGT didn't catch the problem then all the strikes after the problem occured will be the error, and the first strikes will be in short supply.
It will all depend on IGT'S quality control to see which one has the fewer numbers.
Walt