They'll acknowledge that smoking cessation (to be fair, they had a bit to do with this too) accounts for some of the decrease.
But is that accounting for every factor likely to be significant? Most people who had heart attacks In New Zealand prior to 1984 went through the Great Depression, World War 2, and the 1951 Waterfront Strike. They had parents who lived through the 1919 influenza outbreak. Their lives were different in many ways from those of the generation dying early or living longer today.
One of those differences is environmental - the toxicity of industrial, urban, and rural environments has changed, mostly for the better; testing and legislation is mainly a product of 1970's environmental activism. And particulate vehicle emissions, to give the best-researched example, do seem to be causative of atherosclerosis. The last few decades have seen tighter and tighter restrictions on vehicle exhaust emissions on our roads and on the burning of fossil fuels and wood in private fireplaces in our cities.
Another change is genetic - in 1984, Wang was not the most common surname in Auckland. New Zealand has always had a small population, with a tendency for Kiwis to seek their fortunes offshore, and this loss has been offset and the population increased steadily through immigration, with the migrants' countries of origin altering over time.
Another change is in the micronutrient content of the diet. In early days, the poor were at more risk of deficiency diseases than they are today. Vitamins and minerals are added to junk food to give the advertisers something to boast about, and even to improve shelf life; the use of ascorbic acid as an antioxidant (E300-304) is no doubt a safeguard against scurvy in the least-well fed populations.
This change also applies to wholefoods - since the 80's, NZ's importation of foods - esp grains, legumes and fruit has increased, which means a wider spread of micronutrition. There is a wider variety of foods, and of ingredients; market deregulation since the 1980's means the New Zealand food environment has altered significantly.
See, for example Medsafe on selenium
Result? (or, correlation?)
This, of course, has been attributed to lipids and SFA too - selenium has been completely forgotten, it seems - but this was a huge, and brave, public health effort in Finland, comparable to iodised salt being introduced to iodine-deficient societies in the 1920s. And matched by what NZ has done, albeit by chance more than by design. Finland was one of Ancel Key's strongest statistical supports - and the methodologically questionable Finnish Mental Hospital Study is still a mainstay of lipid hypothesis epidemiology. We are not talking selenium supplementation above requirements, which doesn't prevent CVD, but correcting selenium deficiency. (If you ask me, the micronutrient theory of diet-health correlations is sadly neglected at present. What slows the oxidation of lipoproteins? Not so much any antioxidant tested separately at megadose intakes - just the whole antioxidant defense system working smoothly on a little bit of everything it needs. Selenium, zinc, etc., etc., etc.).
2014 is not just 1984 with less saturated fat.
There is more detail about the Finnish selenium program here.
I bought this 45RPM record at a thrift shop the other day. Blue Band, by Bobongo Stars - the full version (it covers both sides) is pretty cool, with a great old-school synthesizer solo. The story of the song, and of Marsavco margarine is told here; it's a palm oil product (so not much need for hydrogenation), and today it's fortified with vitamins including nicotinamide; probably a good thing in the corn-eating regions of Africa. The song is credited to Marsavco-Zaire.