This classification is primarily based on the research and publications, including a dictionary[1] by Dr. Adam Wrede (1875-1960), a linguist at the University of Cologne.
The Old Colognian language developed later than the 12th century,[3] evolving from a mixture of the then old fashioned Ripuarian and Low Franconian dialects and Old High German.
It was the language of the Electorate of Cologne, spoken and written every day by both the ecclesiastical and secular authorities as well as the residents of the city and its surrounding area.
So it was very well preserved through the Middle Ages and into the Modern times, with a rich variety arising from everyday use.
[5] During the 16th century, the influence of the New High German language increased in Cologne and along the Rhine River, changing the way of writing used by the monasteries, authorities, and printers.