It doesn't work that way. You don't hold a cert for a particular week. You hold a cert for the chance to play there. Then you submit your application with weeks you'd prefer and CDP responds by assigning you a week once they sort out the schedule.
These certs are like gold. There are a finite number available.
The reason I asked what week it was for is because the time to send in the certificate had passed. The weeks had already been handed out when they sent out that post. So if they didn't send in money and the certificate already, then that piece of paper isn't worth a thing.