You will be assigned a new CDH if your membership was expired more than six months ago. Your old details may still be used for determining the new handicap though, and your old history can be found by the new club given the relevant information of your old club.
Yeah the 'lifetime' part of it is a bit peculiar as its only relevant if your in continuous membership. After six months a new number is issued ... at least that was my understanding, unless they've changed that recently.