In assessing the value of any historical work it is necessary for the investigator to undertake the often frustrating and tedious task of Quellenforschung. In the case of the De Caesaribus the first substantial attempts began in Germany in 1873 and 1874 with the appearance of two important studies by A. Enmann and A. Cohn. Enmann sought to explain the mass of verbal similarities, numerous errors and shared idiosyncrasies to be found in Victor's De Caesaribus, Eutropius' Breviarium 7–10, and parts of the Historia Augusta by postulating a common source which has subsequently come to be known as the Kaisergeschichte. He was so convinced by his findings that he stated (p. 459), ‘Victor und Eutrop es beide als Haupt – wenn nicht als einzige Quelle benutzt haben’.
Working quite independently Cohn's examination of the first eleven chapters led him to conclude that from the beginning of Augustus' sole reign to the death of Domitian Victor, Eutropius and the Epitomator followed a common source which he entitled Suetonius auctus, an account excerpted from Suetonius with some new material added. Enmann, however, had already described the Kaisergeschichte's early chapters in this way and the two were readily identified.
One major problem remained. The traditional date of the completion of the HA was still believed to be 305/6; consequently if the K.G. had been used by its authors then the K.G. must have been written by that year. Nevertheless notable similarities between Victor and Eutropius continued apparently till 357 and Enmann therefore suggested a continuation of the K.G. until that date.