We had signed up for the max for Postcard exchange #27, but when I checked my address list against the list on the APUG website, I noticed you were not on it, so I got your address from the last round and sent you our postcards! I may have misunderstood the rules, but not to worry, you are not in our debt.
As Uwe said, we can run out of pairs before the "MAX" or even some of the higher numbers a met. However, I don't believe there is any "rule" that says you can't send extra cards, so feel free. BTW your cards have arrived safely on the east coast!