Understand that DoDMERB clears a candidate based on the requirements of a specific location(USNA, USMA, NROTC, ETC). West Point may have different requirements than the NROTC. NROTC may have different requirements than USNA. Though they might be similar, they are not universal. A DoDMERB physical is good for 2 years, but each selection location still has DodMERB check to see if they are qualified. So if he was found qualified by DoDMERB for West Point(and I think you imply that) that does not mean he as been found qualified by NROTC. He should be able to go onto his DoDMERB account to see if NROTC has requested a check.
Are you sure "they" is from NSTC(Great Lakes) and not DoDMERB? NSTC doesn't usually ask for this type of info as that is what DoDMERB is for. NSTC just want a completed sports physical from a doctor (which your son should have included with the other info he submitted) Look at below.
from the 3rd page medical requirements:
"To be medically eligible to participate in NSI, you must complete a Pre-participation
Physical (Sports Physical) signed by your primary care provider and you must be medically
eligible for all sports without restriction during the current school year (15 August 2023 to
present). If you’ve suffered an injury that required surgery or physical therapy, you must get a
new sports physical. If you are not medically eligible for all sports without restriction, you will
be on medical hold until your DODMERB physical is complete and you will be required to
attend NSI the following summer.
All Midshipman Candidates are required to provide a copy of their immunization record
as proof that they have received all mandatory vaccinations listed on the NSI Package Checklist.
A newborn sickle cell blood test is also required prior to participating at NSI. If your Sickle Cell
Test (SCT) is positive, please contact the CMGO for further guidance."
You might want to have your DS check to see who is asking for this information. Regardless of who it is though. He needs to assist in providing them with the info they are requested. It doesn't have to always make since why they want it to your son. He just has to do it. It is good training for his future military career.