There may not be one. I agree it is unusual to have a DC without a cause of death ... but
in 1972 the british authorities here may have had little desire to enquire into a cause of death abroad.
I recorded my fathers death in that year 1972. It was only paper work, we were desperate to get on with things and didnt want a coroner involved. The registrar ( hand in the doctors cert and you get another one which allows you to apply for probate and do a funeral etc) grunted and said - he was a doctor here wasnt he? I said yes. My mother commented they knew each other for forty years. Things were like that then. And hadnt changed much in 1995 when my mother died.
2015 - awful hoop-la. Post Shipman and no one wanted to certify anything. Jobsworths pay scales, do nothing and procrastination.
Having visited the consulate in Athens, 1973 , they said they didnt assist ex pats and wouldnt let us in ! A clerk ( third undersecretary's bag carrier) had a chat with us in the street outside, wished us well and popped back inside
I know you suspect that they had info that they covered up
but it is much more likely they knocked off early, went down to the cantina and started on the ouzo....It was like that then