The area has changed. However the inhabitants don't know this. 300 years is a long time. People change. The area in Lower Darby along the river is now a peat bog. Lower Darbians slave away mining the bogs for peat. The Darbians essentially have the wealth and the Lower Darbians essentially only have one cash crop: peat.
Darby is known for its beer - which is brewed with the stolen Barley seed to the east of Darby. It is still called Nuoc Mam but it is not the great Nuoc Mam of long ago. But this is unknown to all but the Brewmaster of Darby.
Meanwhile in Lower Darby...A peat miner, Bogdog Gristlehand, finds an old box preserved in the bog, among some old structures. He opens the box and sees a book of recipes for beer and the like. Of course, he can't read it. He also finds a few bottles of the old brew: Nuoc Mam Pilsner, Nuoc Mam Stout and Nuoc Mam Porter. The labels have the three fish symbol. He can't help blabbing about his find. His boss, Bogalpha Opportunbeard, overhears the tale. So he takes the box and book from Gristlehand - Opportunbeard doesn't know about the beer. Bogalpha sees that the book is a recipe book for brews but doesn't understand its significance. He does however realize that it shows that the old structures in the bog must have been breweries. But why? Why in a bog? He also notices that the symbol on the front of the book (3 fish arranged in a ring, head to tail - not colored). He deems this important - but isn't sure why, it vaguely rings a bell of some children's rhyme. Why? Sensing a reward, he turns the box and book over to the city council of Lower Darby.
The council is wiser. They realize that some of the recipes are for Nuoc Mam. But how can that be? It describes special harvesting procedures, it also indicates the Lower Darby used to be a fertile place, and that the grain grew in Lower Darby - NOT Darby. It also mentions that the grain had to be harvested with the assistance of the head Fish Friar. Those whackos?