I don't think you actually have one of the problem d600's.
The problem ones don't have a 'dust' problem per se - at least not any worse than most modern DSLR, they have an issue with debris and lubricant being thrown on the sensor. The spots are quite a bit bigger than dust spots and are visible at much wider apertures.
I returned 2 D600 with this issue. I mentioned this before, but I think there is some semantically confusion involved as this issue has become known as the 'dust' problem - when the reality is something different.
While there is no doubt that Nikon will repair any camera with this problem under warranty, their policy requires that you pay for shipping.
I agree it is a communication problem from Nikon. They meekly admitted this issue and then faded into the night. If they just came out, made a definitive acknowledgement and then advised when the problem was fixed we could all move on with our lives. Instead we are doomed to years of threads about whether Nikon ever fixed this - and who can blame someone for asking - Nikon has done a lousy job of keeping people in the loop.
I would simply buy local from a seller with a window to exchange for manufacturer defects - my local one gives 10 days. There are many good d600s out there and you are likely to get one. If not, exchange it until you do. If your d600 has the issue, you will know fairly quickly. Both the ones I took back showed it within 300 shots.