Well, I'll probably be too obvious here, but begin at the beginning: all errors are mine, all good data is from Kingslake, Schwalberg and others.
We know D A G O R represents Double Anastigmat GOeRz.
We know that a double anastigmat can be in several forms. Goerz made more than one form of double anastigmat. The other double anastigmat Series included an f/4.5 dialyte ( double anastigmat Goerz type B ) and and f/6.8 ( type C ).
In 1904, Goerz renamed their lenses, thank goodness. The Series III Double Anastigmat Goerz became Dagor; Type B became Celor; Type C became Syntor. It was for more than convenience: everybody and their cousin was marketing Double Anastigmat lenses at the time.
Series III is always the DAGOR we have in mind when we think DAGOR. All Dagors are Series III ( and all Series III are DAGORS ) which in the USA said Series III until post WW2, when the Gold Dot and Gold Ring Dagors came into existence to combat the marketing of war surplus Dagors, and various government contract Dagors ( some of which are among the worst lenses ever made, and are still, sadly, circulating in near mint condition on Ebay ). The Gold Dots and Gold Rings are simply Series III lenses, with coating, and cosmetic differences. The Kern made Schneider Dagors are American Optical Series III lenses. The last of the Kern lenses have less coverage due to the limitations of the Compur shutters.
Goerz began business in the mid 1880s. ( give or take a few months ) and manufactured a range of lenses including landscape objectives, an aplanat called the Paraplanat, and a rapid rectilinear lens named Lynkeioscope, designed by Carl Moser. Goerz hired Emil von Hoegh in 1892, who had tried to get a job at Zeiss and failed. Von Hoegh happened to have a design in his pocket which he presented to his new employer: the 6 element double anastigmat. Moser died in 1892, and was succeeded as head designer by von Hoegh, who retired in 1902, and died in 1915. In the '20s, Goerz was one of many small forms who were amalgamated into the Zeiss combine.
One of the early products of the Goerz company was a fine camera, designed by Ottomar Anschutz in 1884. The Goerz/Anshutz camera had a focal plane shutter, with a top speed of 1/1000 of a second. The ANGO was a real sweetheart of a camera, and Anshutz a remarkable man in his own right.
Attached is a snap of Otto Lilienthal made by Anshutz in 1894, hopefully with a Dagor.