[mohaine]

They were actually changing the deck in way that survives shuffling, not just looking at the differences.

They were using the offset on the printing as a way to tell orientation of the card. Since auto shufflers never rotate the cards, any rotation they added would persist allowing a way to tell good from bad cards in future hands.

[zos_kia]

Yes that is why I mentioned it was nearly impossible to replicate. The final optimized method involved a lot of social engineering, which required to have very high standing in the casinos. She had to request, under the guise of superstition, a specific setup with a specific style of dealer, who never changed decks, and to be authorized to call out certain cards as "lucky" which the dealer would flip themselves.

It also required deep pockets, as just playing the shoe enough to sort it could take a few hours of regular gambling. That's the crazy thing, this elaborate setup just got them a few % edge on the house which they milked relentlessly.