Wow, great question.

Unfortunately, I can't help on that one, my knowledge just isn't strong enough. I would assume the double nights count from the moment they go on your record for 12 months, but they could easily program the computer to wipe off the double nights at the end of the year.

My reason for posting is just to say that you're not alone, but it is unusual to find a new thread on this site left unanswered for over 24 hours, and felt it unreasonable to let it drift unanswered off the frontpage. Hopefully my reply will give it another 24 hours on the frontpage, for those far more knowlegeable than me to reply...