Just called again and another agent quoted me 195K miles/person if I include CZ in my itinerary. She transferred me to rate desk's agent who told me that extra 45K skymiles are required because china southern has special dates on which you cannot combine them with another DL flights at low mileage. Aka blackout dates. Since I'm looking for new year 2014 travel, sure enough december 7 - january 6 are forbidden days for CZ.
Is it true? I never heard about such rules.
That's just a load of nonsense. Ask the agent where are they actually getting that from and ask them to point you to that, and/or to forward you the fare rules over e-mail if you can't see it online (as you can, though, normally) as you'd like to see it in writing. In the published award fare rules it certainly doesn't state that; there are blackout dates only for CI, AE and KE. If there are any such dates, it must be published. Here it was just a lazy agent who was ready to say anything just to get you off the phone so that they could get away with not doing your job, plain and simple. Either that, or a very incompetent agent who has not the slightest clue of what they are doing.