Country
Only count experience with employers who you believe will agree to provide an Employment Verification Letter that proves the dates of employment and job title.
E.g. has anything you worked on been mentioned on a grant application that your superior or advisor submitted to obtain funding for a project? If you don't know, ask your superiors.

I agree to terms & conditions provided by the company. By providing my phone number, I agree to receive text messages and calls from the business.