Nothing says "Please scrutinize me further because I'm actually tailormade for a Visa Case Officer" like putting the actual NOC in the experience letter. DON'T DO IT.
The idea is that whatever letter you still get out of the companies can be useful in your day-to-day life - adding context-specific information like NOC code, Express Entry Profile number, UCI number (if you know it), does more harm than good and is just a waste of company goodwill trying to get it. Not to mention it'll just arouse suspicion from the legitimacy of the document because really, who gets an experience letter made like that with Canadian immigration specifically in mind?
It'd be different if it was a LOE from the company, attached to a standard reference letter to explain something that wasn't covered in the Reference Letter but the company's policy isn't allowed to actually provide in writing. But otherwise, a definite no-no.