When I recently booked and then canceled a 35K FNC night, the certificate didn't go back into my account - the rep couldn't get it back, but he was able to give me a new 35K FNC - which was therefore good for a year from that date. That worked out well, it means it will overlap with another 35K FNC. (I know they're less useful post-devaluation, but 2 nts is more useful to us than 1 nt)

I wonder if the same thing happens if you book and then cancel a 7 nt reservation before detaching the cert - the difference being that the reps may not have any familiarity with the 7 nt certs, so that once the cert is lost, it stays lost.