For my three-card ballot I cast on Tuesday, here's how each card was numbered (per the strip torn off each card I got to keep as a sort of receipt):
Side One: A-Card 1, [number1] [(number2)] [number3] BT:3 (right side)
[number4] - POLL, [number5] [barcode square graphic]
Side Two: [number4] - POLL, [number5] [barcode square graphic]
Side One: B-Card 2, [number1] [(number2}] [number3] BT:3 (right side)
[number6] - POLL, [number7] [barcode square graphic]
Side Two: [number6] - POLL, [number7] [barcode square graphic]
Side One: C-Card 3, [number1] [(number2}] [number3] BT:3 (right side)
[number8] - POLL, [number9] [barcode square graphic]
Side Two: [number8] - POLL, [number9] [barcode square graphic]
There were three numbers consistent between the three ballots, and two which were unique to the ballot. I believe the "BT:3" indicated there were three cards per ballot.
Ack. I meant to say, there were three numbers consistent between the three CARDS, and two which were unique to each CARD.