Best individuals to interview for my UX research

I'm at the early stage of preparing a usability test with several individuals. One of the pages we want to test is the accreditation process, used by journalists who wish to get permanently accredited at my organization. I know some journalist willing to help out and be interviewed while performing this task, however I'm afraid the results won't be accurate because most of these individuals have already been accredited, which means they have dealt with that process at least once.

So I was wondering whether it's better to test users that are not journalists? or should I stick to journalists, since they will be the primary users of the accreditation process?

thank you in advance!