Say, for example, a group of people were given the card tag, "Proximity Blue Key Tag", in the link above. This card tag gave access to buildings 'A' and 'B' to those with the cards (card AB).
Another group of people were given the same card key tags, but half of them could only access building 'A' (card A) and the other half could only access building 'B' (card B).
Card keys of this sort are read by the reader following this link: http://www.incontrol.co.nz/products/PRX-TSEC-STD
With all three cards in existence (card AB, card A, card B), how would one with limited access--holder of card A-- access both buildings A and B without using card AB?
Hopefully my question doesn't come out too muddled. A simpler way to phrase it may be: How would one create an RFID master key for a RFID based security/access system?