How old is the oldest jigsaw puzzle?

This is a question I was asked recently, which set me to doing some research...
The Oldest Jigsaws, or dissected puzzles as they were then called, were the dissected maps made by John Spilsbury, map maker and owner of a print shop in Russell Court, London. He was born in Worcester in 1739 and Linda Hannas' book ' The English Jigsaw Puzzle 1760-1890' gives a detailed account of his life.

In 1785 John Wallis published the first really light hearted puzzle 'John Gilpin ' an illustration of William Cowpers ballad.

In 1787 William Darton was the first to dissect a chronological table of English Sovereigns with the grand title 'Engravings for Teaching the Elements of English History and Chronology after the manner of Dissected Maps for Teaching Geography.' The puzzle was as boring as the title, and the next year his rival and neighbor, John Wallis produced a lighter version that went on selling for the next ten years.

I'd love to hear from you if you can add any further thought to this discussion.