At this year's summit, Seoul signed a further deal with Turkey. Australia's talks got back on track about a year ago, although they are now at a stalemate.
Key's fear was that South Korea's appetite for fish would be sated before New Zealand's dish even made it to the table, and his trip to Seoul was as much about ensuring that did not happen as attending the summit.
Signs of that trade were everywhere. There was Anchor butter in the dining area for the 3000 foreign media at the summit. The cafe at the Coex conference centre had shelves of Whittakers' chocolate and Phoenix juice, and Hell Pizza is a relatively recent arrival in Seoul.
Fresh food is expensive in South Korea, and Key made the most of the food inflation issue, driving home the message that New Zealand's seasons were the opposite to the Korean Peninsula's, that its winter was New Zealand's summer - a time of year when its Southern Hemisphere trees were heavy with fruit while those in the north were bare.
He was almost shameless about his pitch, pushing on every button he could find, from sentimentality - a reminder that New Zealanders had died defending Koreans' homeland - to a warning that South Korean tables could find themselves bare of popular New Zealand foods as New Zealand businesses were starved out of the market by high tariffs.
Though Key is strong on trade, he is less adept at the nuanced dance of diplomacy - something he will happily admit to himself.
In Seoul, he was confronted with 52 other Prime Ministers and Presidents. With so many in one place, it's easy to mix up your Presidents with your Prime Ministers - especially in cases such as Russia, where the same two people alternate from one to the other and back again with great regularity.
At least twice, while speaking to the media, an adviser had to chip in to correct Key's affliction of Mixed-Up-My-Presidents-and-Prime-Ministers.
When he decided his speech to the summit was going to be largely unscripted and based only on a few handwritten notes he'd prepared for himself, the Foreign Affairs officials must have trembled in fear.
However, Key does not suffer from false modesty. When asked what he was offering in Korea, he said he had nothing to declare but "my sunny personality". The trip was a rare opportunity to build relations with leaders of major countries and Key was not going to waste it.
There was, of course, one leader about whose title Key had no doubts whatsoever - Barack Obama.
There was an ironic historical significance to the nuclear summit's timing and location which went unremarked on - it was the Korean War from 1950 to 1953 that sparked the Anzus Treaty in 1951, securing New Zealand the protection of the United States.
That treaty lasted until the 1980s, when New Zealand introduced its nuclear-free policy, prompting pursed lips from the United States.
That it is now John Key the money trader who is getting the benefit of the shift in outlook from the United States must be infuriating to the anti-nuclear campaigners of years past.
However, Key's more pragmatic approach to such matters could pay off. Much was made of Obama's invitation to New Zealand in 2010. The impact of that symbolism of New Zealand sitting next to nuclear giants had worn off this time round. But when Obama stood to deliver his closing remarks to the nuclear security summit, Key was one of only two leaders he made direct reference to - endorsing Key's remarks about the worldwide impact a nuclear terrorist attack would have.
Of course, all Key's hard work in both areas could be undone by that pesky feature of modern society known as democracy.
South Korea has National Assembly elections next month and will get a new president in December who could change its outlook on free-trade agreements.
And the United States elections in November could change its current indulgence of New Zealand's nuclear-free stance - whether for better or worse.
It was amusing that of all those leaders Mr Key spoke to, perhaps his most uncomfortable chat was with the President of a country a similar size to New Zealand - Sauli Niinisto of Finland. Mr Key was left to explain his minister Gerry Brownlee's description of Finland as a crime-ridden land of misogynists by explaining that Brownlee was well known as one of Parliament's more-robust comedians.
So Key found out the hard way that in trade and diplomacy, as well as comedy, timing is everything.
