Have been investigating on/off switching in deaths and single-year-of-age patterns. See sections on deaths, etc in the attached list of publications http://www.hcaf.biz/2010/Publications_Full.pdf
It would seem that international periods of higher deaths may have been ignored for lack of a fundamental explanation. See also:
https://authors.elsevier.com/a/1W8Fx3Or0KBpRr
My thoughts need further investigation by those with far more resources than myself.
Kind Regards
Rod Jones