in USA they can fill in 20 secondary causes on the death certificates and all the anonymized death certificates since 1959 are available online from NCHS in computer-readable form to check/search for conditions. Irregularities usually appear when there is a switch from one ICD-Code to a new one, so in 1969,1979,1999. Other irregularities are often checked, compared with other states,countries,conditions and the reason discovered
What if the patient has several chronic diseases that could have been underlying causes of death? Well, you only get to pick one, and only that one gets recorded as the cause of death. You can list the other diseases too, but not as causes of death.
It seems I miscommunicated here. What I meant to say that listing these other diseases has no meaningful impact on the mortality statistics, although technically speaking they are causes of death. If the point is to gather accurate statistics, listing them feels like a consolation prize, because statisticians...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.