[S]ome things about ancient kings that seemed insoluble in the past have been resolved with new discoveries. Thus the book of Daniel calls Belshazzar the last king of Babylon, while the Babylonian records say it was Nabunaid. However, a recently found tablet tells us that Nabunaid gave his son royal power, went to Arabia, and never really reassumed the throne (Cf. J. Finegan, Light from the Ancient Past, Princeton University Press, 2nd. Ed., 1969, p. 228)). So a future discovery may unravel this question about Daniel 1:1. However, we do not really need any of the above at all. We ask in what genre the book of Daniel is written. All admit that there are two genres. One of them is apocalyptic, evidenced in the strange visions. The other is still being discussed. It is known that at least by the fifth century B.C. a genre of edifying narrative, with a didactic purpose, became popular, as seen in the Ahikar story. This genre somewhat resembles a romance or historical novel. It is an edifying story in which there is some fact, especially in the setting, but is a free fictional handling of many things, especially those not needed for the purpose of the work. In such a setting, the dates and names are unimportant. Yes, the writer may have put down what he happened to think about dates, but he did not mean to assert these were accurate, for accuracy was not needed for his purpose. (William G. Most, Catholic Apologetics Today: Answers to Modern Critics [Rockford, Ill.: Tan Books and Publishers, Inc., 1986], 219-20)
Further reading:
Thomas E. Gaston, Historical Issues in the Book of Daniel (a convincing defence of the historicity of the book of Daniel)