Bad batch of cards, or reader/writer issue?

[GreyUser]

What we don’t know is if the cards were readable after writing in those other devices. If they were - then it is card deterioration or demagnetization.

It is doubtful it is the eccentric adjustment. With o-rings, the minimum force setting, where the pimple is towards the card surface (facing the front of calculator and the slot is parallel with the motor driven threaded shaft), is 99% of the time, the optimal position. If the force is too high, the usual result is for the motor to slow down under the load and the track write is not completed before the end of card switch is activated, throwing a write error.