Yes, to answer your original question, which was not covered, if you are merely denied a new TN due to some deficiency in your petition (something missing). However, if you are "personally" denied entry for some reason such as legal trouble etc,, OR they find that you are not really qualified for the TN you are requesting (which they could then call into question your current TN) you will be allowed to continue using your current TN. This would be rare given that your previous TNs were based on your degree and the job description and were successful.
Bringing up the fact that you have a masters and 5 years experience means nothing. You are not interviewing for the job at the border. The company has already done that process. You are simply presenting your degree and the company is presenting the job description.