Originally Posted by
milesmuncher
IME it will simply un-register that card from the previous program (I always get an email notification of this).
I don't think that's the case as it would create a dangerous precedent of un-regestering a primary cardholder of this card without his/her consent in favor of the authorized user (as the dining program has no ways to find out who is the primary cardholder and who is the authorized user). A couple of times I've tried using the same card registered in the other program it simply indicated the card was not eligible.