It transpires that there are actually eight deadly sins - the usual seven, about which much has been written, and the eighth: filling out your Census forms if you are overseas on the day.
So while New Zealanders leaped up on Tuesday morning to tick their boxes, I was scoffing enchiladas de pollo en mole in Mexico City and watching the shoe-shiners at work while my Census forms sat forlorn and blank on the bookshelf at home in Wellington.
Ditto, I assume, for the other 60 or so people on the Prime Minister's delegation to South America - including John Key and his first lady, Bronagh.
Some of the others cocked an inadvertent snook at the rule - filling out the forms and cheerfully writing "Mexico City" when asked where they would be on Census night, if not at home. Others took on the role of conscientious objector, filling out the forms in blatant disregard of the rules.
One man on the trip had got into a blazing row with the Census worker who arrived at his house. Upon being told the man would be overseas but still wanted to fill out the form, the worker refused point blank to hand it over or give him his code so he could do it online.
It is not clear whether it is against the law to fill out the forms if overseas. However, Statistics New Zealand told me it would prefer people overseas to refrain from doing the Census, even though (because of the online service) you no longer had to be there to have the form picked up. The reason was that the Census was intended to be "a snapshot in time".
The problem is that the figures from that one day are then used for the next five years' policy-making and important matters such as electorate boundaries, and the number of Maori seats.
I, however, will not exist for the next five years and my house will be an "unoccupied dwelling".
The United States does not have such a silly rule and hasn't since its first Census in 1790. Then it established the "usual residence" rule, so that people who were not at home on Census night - including those on overseas trips - would be counted at the place they usually lived.
It has special rules for people who live in more than one house - such as "snowbirds" who migrate to a warmer place for the winter.
That first Census in the United States took 650 federal marshals 18 months to do, cost $45,000 and discovered there were 3.9 million people.
Things are a bit quicker now and more expensive (the 2010 US Census cost $13 billion) and there are more people (309 million, in fact).
It remains a mystery why New Zealand cannot manage the same thing in the 21st century with a population of more than 4.4 million and the wonders of modern technology.
It seems a paltry issue, especially given my confession that I was swanning about ancient cathedrals, and sitting in that little restaurant testing the mole sauce instead.
Admittedly, I would not have sacrificed that in order to answer questions about whether I lived with four people, or, in the rather dispiriting words of the Census "none - I live alone".
But were I, say, a Cantabrian, or a Maori on the Maori roll, I would be frustrated.
I like the Census. It reveals all manner of interesting information about our society - from the number who write down their religion as Jedi to whether the man-drought has worsened or improved since the last Census.
Mexico holds a Census once every 10 years. Among the finds of the last one in 2010 was that more of Mexico's 112 million people had televisions than fridges or showers and only 6 per cent of people lived in homes with dirt floors - down from 20 per cent in 1990.
The United Kingdom's Office for National Statistics website reports that in ancient Roman times, the Census was used to determine taxes, listing every person in a household and any properties that could be levied.
I think I can safely say that if raising taxes was still one of the purposes of the Census, those of us overseas on the day would not have been able to escape easily.