In the last 21 hours my illustrated inquiry on Reddit's Liverpool subreddit has clocked over 8,600 views, 21 upvotes, and two reasonably useful responses!
My new information includes these reports:
In 1867 John Duncan ('fish dealer, St John's Market') was summonsed to court after selling salmon suspected to have been poached from the River Dee without permission. It seems like there was a considerable argument over whether it was Irish salmon or a Dee salmon, with heated discussions over the pattern of the scales, etc!
[Poached salmon?]
In 1887 John Duncan, JUNIOR, was a Liverpool councillor representing Lime Street Ward.
In 1889 Junior was living in Victoria Road, Waterloo, identified as a fish dealer, and was nominated for re-election.
Fast forward through lots of newspaper ads to 1950, when a John Duncan becomes president of the Liverpool Wholesale Fish, Game and Poultry Merchants Association.
In 1958 John Duncan & Sons Ltd, is advertising as "fish, poultry and game suppliers" to restaurants from their headquarters at 23 Great Charlotte Street.
In 1964 John Duncan, age 56 and the fourth generation of his family in the business -- which was established "over 150 years ago" -- becomes the new President of the UK's National wholesale fish trade association.
1966: After 83 years on Great Charlotte Street, the fish market moves to a new site in Stanley Abattoir. John Duncan (IV?) is photographed helping to move the furniture.
1967: A John McKeown, now a director of the Duncan firm where he started as an office boy, becomes the new president of the fish and game wholesale trade group.
Thus far, despite all this history I was able to assemble overnight, the nearest we've come to establishing a start date for the Duncan seafood dynasty is an article from the 1960's noting that the firm was then 150 years old.
No word either way on whether any Duncans are still selling seafood.
No date for the token yet.
Life goes on...
"If everything seems to be under control, you're just not going fast enough."
--- Mario Andretti