Same here. Sounds like maybe they haven't produced this run yet? Possibly because it's such a popular size, thus a larger batch, they decided to do it later or even last?
Someone a couple replies before yours said they received theirs. NS has already sent out a batch of 158's and I'm guessing that by now they've made batches of every size available. People who ordered the boards earlier on will get the first batch or batches of whatever size they've ordered. If you're like me, and ordered towards the end of the promo, you'll be apart of the last batch (or batches) of whatever size you are.
I'm anxiously patient. I want the board now, it's early/pre season and the man made snow here on the east coast does not go too well with my current board so I'm excited to try out the Cobra. With that said, from understanding NS doesn't produce many boards because it's all in house hand made in a relatively small shop. That piece of knowledge makes it much easier to be patient.