Caluza vs Brown defined what is necessary for service connection: https://asknod.org/2012/02/09/cova-caluza-v-brown-total-recall/
This has to be MEDICALLY Documented in your records:
1. Current Diagnois. No diagnosis, no Service Connection.
2. In Service Event or Aggravation.
3. Nexus, or Doctor's Statement close to: "The Veteran's (current diagnosis) is at least as likely due to x Event in military service"
This is also known as the "Hi