It could have been something as simple as the printing date. Once the cards have been updated the old cards are not allowed for use. If a station hadn't thrown out thier old ones and restocked the plane with fresh cards then it would be illegal to fly. It is up to the F/A to notice if the cards are in compliance or not.

I had this very same thing happen a few months ago. We were taking a E170 from PHL. All the cards were E170 specific. We haven't had that particular card since the E175's came online. Therefore the cards were illegal because they were out of date.

It happens I would say that someone put E140/5 cards on the plane instead of E135 cards. Our cards are airline/aircraft specific but not codeshare specific.