It is true that they are not known in any Greek literature until the sixth century. (1) Simply because a word was not written in a certain language at a particular time does not mean the word did not exist. (2) These are not everyday conversation words and thus it would be expected that they would rarely be encountered.
(3) It is not wise to take a stand on the date of a biblical book based on only two or three words.
In other words, it is a conclusion, not an assumption.The Date of Daniel One of the arguments put forth which seems to indicate a late date (second century BC) for Daniel is its place in the canon.English versions of the Bible are based on the canonical order given in the LXX.However, the weight of the linguistic evidence suggests an early date. Approximately half of the twenty Persian loan words found concern government officials in some way.In the entire Book of Daniel only three words are of Greek origin.