They usually add about the flights about 6 months out. How far out are they right now. If it's October now, I'd say that by June you should see December.
I bought Jan tickets in May of 2003 for 2004, be on the look out from early to mid May. They will open 2 or 3 months at a time with a lead of 9 - 10 months open. This has been the pattern for the last two years.