My apologies for the confusion. I meant to say that many NOCs on CIC website have overlapping job duties. For instance, if a person is a management consultant and works for clients across different industries, he could be eligible for an investment analyst or a statistician or economic analyst; it was true atleast in my case. It could be different in engineering and doctor fields. But yes job duties must match at least 70% of the ones listed on CIC given NOC. On the other hand, if your job duties match with multiple NOCs then you could choose whatever NOC you think is best. I do not mean that a doctor could apply in the category of an engineer. I hope it clarifies the confusion.you are mistaken about NOC, the NOC under which you applied must have around 70% matching job duties with the work that you showed and gained points for while creating express entry profile. They are very serious about it.