Assuming by 'existing experience' you meant the ones you put in 'work history' and aim to claim CSR points from. If that what you referred to, all of your documents should serve to support below:
1. You did have these experience and they exactly match what you stated - offer letter, contract, payslips, relieving letter, appraisal letter, whatever
2. Your experience meaningfully matches what CIC required - this is the tricky part. You have to show CIC that these experiences match how CIC define a job that makes a candidate qualified to apply for immigration. That's why the NOC codes are used. If you claim to have 'financial analyst' experiences (NOC XYZ), your experience letter, from a credible source, MUST provide details of your job duties, and these duties must be similar (not identical though, otherwise it seems fishy) to what that NOC says about the job. That means not any random experience letter can be used for this purpose. It must contain details to support your claim that you had worked in an NOC XYZ job for said period of time.
On your second question, it really doesn't matter whether your letter mentions the NOC code or not as long as the detailed duties match the NOC you picked to apply with.