Most important is to make sure that your employment letter which has "Designation", "Duties Performed" matches with the NOC code.
I want to give a hypothetic situation:
Your employer brought you to canada on a work permit valid for 2 years. And your designation was a software engineer with NOC code 2173. In 2 months you get a promotion and become project manager with NOC code: 0213". But you will only be having old work permit which states that your NOC code is: 2173.
So my assumption is, you can be a manager with NOC code 0213 and declare it in the forms for PR and still have Noc Code: 2173 in work permit.
This is just my assumption. I can be wrong. Please ask CIC officials. Customer Service ppl. will not be able to help you. Ask the nearby CIC office.
Or as the other person mentioned, you can get the employment letter with duties of NOC Code 2173, if you can do it. In that case, the letter should mention that your designation is, "Software Engineer".