You will need to negotiate and secure a guarantee on getting the release letter if your residents permit is still not up. Even if the school only gave you a 1 year residents permit with annual renewals, you will still need a release letter. The reason is, everything in china now is digital. Because of this, they can search and see where you have worked in the past. Maybe they cannot do this for schools you have worked at 5 years ago, but certainly they can find out for more recent ones. Employers everywhere in the world now ask for reference letters, anyway. Getting a release letter plus the recommendation/reference letter is always a good idea.

A plus for you would be to scan those documents and save them on your computer and back them up on a usb drive. Whenever you apply for a school, include the pics of the recommendation letters and release letters. That will be an advantage for you.