Evidence is required to substantiate a claim. The evidence must show you have an injury or disease that began or worsened during military service. Or that there was an event during service that caused injury or disease.
In the case of an asbestos claim, the event is the exposure to asbestos while on active duty. The VA will review asbestos exposure during and after military service. A veteran must prove the disease stemmed from exposure during active duty. Medical records that prove a diagnosis of an asbestos illness are required.