As best I can tell, CO does not follow much rhyme or reason. However, many claim that DL does follow the 330 day release schedule and that if you want to play the game, trying for a DL flight at that point might be a good option. Otherwise, do what I do, look up in the Skyteam timetable for every conceivable routing (and don't forget AS, VS, or others if appropriate), and then keep calling every once in a while, going through the routings one-by-one with an agent until you get something.

Link to ST timetable. Note that you want to use the advanced tab to get the most options.
http://www.skyteam.com/EN/travelPlan...bles/index.jsp

I've been doing this since January for tickets from Copenhagen to BKK. I got the dates I wanted after a mere 4 months and perhaps a dozen phone calls. Now I just have to keep at it to try and get something in biz...