Is is possible for the FBI to use a 3 year old medical record from another agency as part of their background check?
Possible? Sure, why not.
Yeah, I just confirmed from a good source that they wouldn’t use medical record from another agency.
No, this is not likely at all. I am not sure if you are asking if the FBI would use part of a 3-year-old investigation or just a stand-alone medical record. They would likely bring your investigation up to date (depending on clearance level) if it is 3 years old and they would not use a stand-alone record.