Now I can't get past the notion that this miscalculation holds the key to many of our social infrastructure problems in 2019.
If that was the population assumption policy makers were using, then of course we have a housing shortage ... of course our roads, our hospitals and our schools are crowded.
I accept there's room for debate about numbers and pace, but in my lifetime this country has been vastly improved by more people and more cultural diversity.
The big issue is the failure of governments, on all sides of the political fence, to plan for this level growth.
Clearly that 2004 population projection was a run-of-the-mill press release at the time.
Reflecting the conventional wisdom of the day, it hardly troubled headline writers.
The projection assumes that the population growth rate will slow steadily, because of the narrowing gap between births and deaths, and the annual net migration rate will be around 10,000.
In fact, net migration has averaged about 25,000 for the past 15 years and has been closer to 50,000 for the past seven.
I'm not having a go at Stats NZ, either.
Forecasts are based on historic models. All we have to work with is hindsight.
Historically, New Zealand went through extreme cycles of net migration gain and loss.
In the last third of the 20th century we experienced regular recessions and suffered from "brain drain" as many of our youngest and brightest headed for Australia or the UK.
But that hasn't happened this century. There was one short, shallow dip into negative territory between 2011 and 2012.
Something structural has changed.
New Zealand just isn't a place people want to leave any more.
Young New Zealanders aren't departing like they used to and the rest of the world is more interested in coming here.
What happened?
In a new book (Narrative Economics), Nobel prize winning economist Robert Shiller puts the spotlight on the power of stories to change fortunes in ways that traditional economics can miss.
I think the New Zealand story has changed in a profound and historic way over the past two decades.
Last century, New Zealand didn't figure at all in the thinking of the Americans or the Chinese.
When we featured in British and Australian thinking, it was as a dreary colonial backwater.
If we had a place in the world it was very small and almost always on a sporting field or in a sheep joke.
Fast forward to 2019.
New Zealand finds itself being cast as the "woke" capital of the world.
"Moving to New Zealand" has become a running joke for liberal celebrities talking about a Donald Trump win in 2020.
A Green MP says "Okay, Boomer" in parliament and it makes The Washington Post.
Presidential candidate Bernie Saunders says he wants to follow us on climate change legislation.
Indie filmmaker Taika Waititi is the darling of Hollywood's cool crowd.
Director/writer/producer Taika Waititi arrives at the Los Angeles premiere of his new film Jojo Rabbit. Photo / AP
Our Prime Minister is a star on the top-rating American talk show.
We're a bolthole for apocalyptically minded billionaires the world over.
Never mind the child poverty stats, the UK and US media simply can't get enough of the notion that this country is a liberal paradise.
Never mind the polluted waterways, Chinese media love the narrative that New Zealand is the cleanest, greenest producer of the healthiest food on Earth.
Of course, there are other factors to our steady economic growth.
The rise of China's middle class and our signing of our Free Trade Agreement were timely.
Prices for export commodities like dairy, meat, wool and wood were regularly written off by commentators 20 years ago.
Economists assumed they were all on a downward trajectory - only wool followed that script.
Australia becoming a lot less friendly to New Zealanders has influenced our net migration rates. It's not nearly as easy to enjoy the easy life across the Tasman as "Bondi bludgers".
Tourism has boomed - although that really goes hand in hand with the rise of New Zealand's story.
That story has been the magic ingredient driving a staggering rate of population growth.
Demography is destiny, sociologist August Comte once said.
Now more than ever New Zealand has some control over that destiny.
We can choose to turn the immigration tap up or down with policy settings.
We have choices because we can rest assured that the demand is there.
But we need to watch closely and challenge our assumptions as our story evolves.
The powers that be didn't pick it 15 years ago and we have failed to plan adequately for a long boom.
That failure has been in part due to a lack of confidence.
We assumed the brain drain was still an inevitable part of our story.
We failed to see what a desirable place New Zealand has become in the eyes of the world.
