Good question Andy and a point i did not expand on from my research, yes a lot of unexplained death is because of a lack of necropsy's, "BUT" here is the kicker, in about 90+% of the necropsy's i read about it was a jaw to vent incision with inspection of the organs, gut cavity, trachia and digestive tract with a possable microbiology but did not include spinal inspection or craniotomy, so i suppose it is up to the individual to ask their vet to include these other tests, although i feel most vets would charge a fortune to do these extra's, so then it is just unexplained death, IMO (and others i have read about) a proper necropsy should include spinal and cranium.
.................................Ron