New TN application with previous employer

I have a job opportunity beginning in January with an employer I just completed an 8-month internship with. It is a similar position to what I had but it is a 1-year internship. I am just wondering how the employment letter needs to be structured being that I have previously worked with TN status for this employer. Does the previous internship have to be mentioned? How can we make it completely clear that this is only temporary? Does anyone have an example or some useful tips?

Thank you.

The TN Visa letter's purpose is to show the Immigration Officer how the job meets the NAFTA Occupation requirements and that your education/work experience is sufficient to meet the job requirements as well as you qualify under NAFTA.

The internship may or may not be mentioned based on the above.

Here are some articles to help you:
Common TN Visa Mistakes to Avoid

Write a Great TN Visa Employer/Application Letter

Good Luck.

I don't see the relevance of the internship to your new TN application.