brewmeist - your son is at an SA, right, forgive me, can’t immediately recall which one.
Some thoughts:
Has he ever logged into DFAS My Pay? One of the many options is verification of military employment. There may be something there that helps. His SSN will be the verifier.
The “orders” could be construed as the Permit To Report (USNA) or other SA equivalent. Was there a cover letter welcoming him and directing him to report?
The USNA Midshipman Personnel/Pay Office, or the equivalent at other SAs, should be able to do a letterhead statement of verification of military status and assignment in MD. That’s a routine task. Military folks need those for various reasons. I recognize there is a challenge with the being away from the school right now. If he can contact his chain of command, the officer or senior enlisted, and ask if they could get a verification of military status and current duty assignment statement.
Is your state one of the ones that doesn’t assess